NEW YORK, August 7 (Praxis Press) By 1950, about 80% of men and 40% of women in the United Kingdom smoked, but decades would pass before the health effects of long-term smoking and smoking cessation could be quantified. Peto and colleagues studied national trends in smoking prevalence and lung cancer rates. The epidemiologic study included hospitalized patients with and without lung cancer in 1950 and 1990; it also included 1,465 case-control pairs from the 1950 study and 982 cases and 3,185 controls from the 1990 study. The estimated risk of dying from lung cancer by age 75 years increased from 6% in 1950 to 16% in 1990 among male smokers and from 1% to 10% among female smokers. However, in 1990, both male and female former smokers had markedly lower rates of lung cancer when compared with continuing smokers. As a result of cessation, only about half of the predicted lung cancers actually occurred in 1990. The cumulative risks of lung cancer by age 75 were 10%, 6%, 3%, and 2% in men who quit at ages 60, 50, 40, and 30, respectively. Smoking cessation has created a gap between predicted and actual lung cancer rates in the United Kingdom; quitting, even well into middle age, has a protective effect.