Plasma cholesterol levels were measured in 15,892 participants of a cholesterol screening in Hartford, Connecticut. The screenees were typically health conscious as evidenced by the low prevalence of current cigarette smoking (12%). However, more than 25% of the men and 35% of the women over the age of 50 years had cholesterol levels in excess of 240 mg/dl, placing them at moderate to high risk for coronary artery disease. Results showed a pronounced dose-response relationship between cigarette smoking and cholesterol levels in men of all age groups and in women of premenopausal age; however, average cholesterol levels were similar in exsmokers and subjects who had never smoked. Risk analysis revealed a strong positive association between cholesterol and prevalence of nonfatal myocardial infarctions. Notably patients with newly diagnosed hypercholesterolemia reduced their cholesterol levels an average of 40 mg/dl under the care of a physician. These results indicate that cholesterol screening coupled with physician follow-up and treatment can have a substantial impact in lowering cholesterol levels and the attendant risk of cardiovascular disease.