ATLANTA (CNN) -- Before Dr. Luther L. Terry, then the Surgeon General of the United States, issued his office's first "Report on Smoking and Health" more than 30 years ago, thousands of articles had already been written on the effects of tobacco use on the human body.

Tobacco companies had countered the reports -- which purported to show links between smoking and cancer and other serious diseases -- with denials and competing studies.

So in 1964, Terry and his Advisory Committee on Smoking and Health knew they were stepping into a major pit of controversy when they announced "cigarette smoking is a health hazard of sufficient importance in the United States to warrant appropriate remedial action."

It was America's first widely publicized acknowledgment that smoking cigarettes is a cause of serious diseases.

But the issue wasn't settled in 1964, nor is it settled in 1997, despite literally thousands more studies -- and litigation that has forced at least one tobacco company to admit what some activists say they knew all along: cigarette smoke is hazardous to your health.

More than 30 years -- and more than 20 Surgeon General reports -- later, the issue appears headed for settlement in the courtroom rather than the laboratory.

So what are the risks? Here's what tobacco's critics say:

CANCER

The Centers for Disease Control and Prevention says cigarette smoking is responsible for 151,322 cancer deaths annually in the United States. Most of those -- 116,920 -- are from lung cancer. The CDC says men who smoke are 22 times more likely to die from lung cancer than non-smokers. Women who smoke are 12 times more likely to die from the disease.

Statistical studies have long shown that people who don't smoke live longer than people who do, and scientists have seen statistically the correlation between smoking and incidences of lung cancer since the 1950s.

But a study earlier this year by Gerd Pfeifer of the Beckman Research Institute pinpointed specific carcinogens in cigarette smoke that target parts of a gene already known to be prominent in some cancers.

Pfeifer wrote in Science that cigarette smoke causes changes in the gene p53, which protects against cancer when normal but promotes cancer growth when mutated.

Another study, published by the American Cancer Society, said that low-tar cigarettes offered no relief from the potential of cancer, and in fact were responsible for a type of cancer that reaches deeper into lung tissue.

Other cancers are also affected by cigarette smoke. An American Cancer Society researcher reported earlier this year that smoking increased men's risk of dying of prostate cancer, while other studies have linked tobacco use to increased risk of other cancers, including throat, breast and bowel cancer.

CARDIOVASCULAR DISEASES

Smoking also has been linked time and again to cardiovascular diseases. Among these, the biggest killer is heart disease: according to the CDC, smoking triples the risk of dying from heart disease among middle-aged men and women.

Studies also show an increased risk of death from stroke, aneurysms, high blood pressure, and other cardiovascular illnesses.

RESPIRATORY DISEASES

Smoking is cited as a risk for dying of pneumonia, chronic bronchitis, or emphysema. The CDC says people who smoke increase their risk of death from bronchitis and emphysema by nearly 10 times.

OTHER ILLNESSES

A report recently published in the American Journal of Epidemiology suggested that smoking increased the risk of developing non-insulin-dependent diabetes mellitus (NIDDM) by more than three times.

Studies have pointed to smoking as a risk in vision loss among older people, mental impairment later in life, Alzheimer's disease and other forms of dementia.

EFFECT ON PREGNANCY

Pregnant women who smoke can pass nicotine and carbon monoxide to their baby through the placenta. Research indicates this can prevent the baby from getting the oxygen and nutrients it needs to grow -- potentially leading to fetal injury, premature birth, or low birth weight. According to the American Lung Association, smoking during pregnancy accounts for an estimated 20 to 30 percent of low birthweight babies, up to 14 percent of premature deliveries, and about 10 percent of all infant deaths.

A mother who smokes can also pass nicotine to her baby through her breast milk.

SECONDHAND SMOKE

The studies didn't just point to the ill effects of smoking on those who smoke -- non-smokers, too, are apparently affected by the smoke from their friends, family members and strangers who light up in their presence.

A steady stream of reports documented the statistical risks of contracting cancer or suffering from heart disease, even if you've never put a cigarette to your lips.

The American Heart Association last fall released a seven-year study showing that never-smoking spouses of smokers have more than a 20 percent greater chance of death from coronary heart disease than those who have never smoked who live with non-smokers. That study gave more impetus to the drive to make workplaces and other public areas smoke-free.

The effects of smoking are hard on the children of smokers as well, the studies say. Dr. Claude Hanet of the St. Luc University Hospital in Brussels, Belgium, said earlier this year that a baby born to a smoking mother "should be considered an ex-smoker."

Hanet's study cautioned that cigarette smoke was more detrimental with decreasing age.

And a University of Birmingham, England, study, published in the British Journal of Cancer showed a possible link between fathers who smoked and an increased incidence of cancers in their children, while studies in the U.S. showed a possible link between smoking and DNA damage.

ADDICTION

Of all the diseases associated with smoking, addiction is perhaps the one that receives the least attention. But President Clinton declared nicotine an addictive drug last August. In March, the Liggett Group, makers of Chesterfield and Lark brand cigarettes, admitted that cigarettes were addictive and cause cancer and agreed to pay about $750 million total to 22 states that had filed suit to force tobacco companies to pay for Medicaid for smoking-related illnesses.

Scott Harshbarger, the Massachusetts attorney general and president of the National Association of Attorneys General, told reporters that the Liggett deal "will produce information that indicates major tobacco companies were fully aware that the product they were selling is addictive, that the product they were selling had great impact on public health."

Other tobacco companies are clearly none too keen on the Liggett deal. For them, nicotine remains what they call a harmless flavor enhancement.

BENEFITS?

Despite the weight of the data about the ills of tobacco smoke, research also shows some occasional benefit from smoking. Researchers at the Brookhaven National Laboratory in Upton, New York, reported that something in cigarette smoke lowers the levels of an enzyme known as MAO B.

This coincides with an increase in dopamine, known for years to be the brain chemical responsible for part of nicotine's pleasure.

Smokers, say the researchers, may have a lower risk of Parkinson's disease, because the nerve disease is aggravated by shortages of dopamine.

And while smoking may be a cause of dementia, it also could be sharpening the mind. University of California-San Diego researchers presented a study to the Society for Neuroscience earlier this year showing that smoking cigarettes sharpens short-term learning and memory among young people.

Researchers in the study, however, cautioned that such benefits don't outweigh the risks of more serious ailments.

ASHES TO ASHES

According to the CDC, 400,000 Americans die each year because they smoke cigarettes, making it the single most preventable cause of premature death in the United States.

Quitting doesn't necessarily help, according to another University of Birmingham study -- at least not if the smoker waits too long. Stroke risk is high for up to 20 years after a smoker quits, according to that study, published in the Journal of Epidemiology and Community Health.

The CDC says that on average, if you smoke, you will die seven years earlier than if you don't.