We studied the relationship of cigarette smoking to the severity of coronary and thoracic aortic atherosclerosis in 116 men who received coronary angiography and transesophageal echocardiography. Severity of coronary atherosclerosis was assessed in terms of Gensini's score (GS), and that of thoracic aortic atherosclerosis was assessed by the average sclerotic length (ASL) and average sclerotic area (ASA). The plasma fibrinogen levels were significantly positively correlated with smoking, and fasting blood sugar levels tended to be positively associated with smoking. GS was inversely associated with serum levels of high density lipoprotein (HDL) cholesterol. ASL and ASA were positively associated with age, fasting blood sugar levels and plasma fibrinogen levels, and these associations were statistically significant. Analysis of covariance was used to examine the net association between cigarette smoking and GS, ASL or ASA controlling for age, total cholesterol, HDL cholesterol, fasting blood sugar and plasma fibrinogen. We found that GS, ASL, and ASA were all significantly increased with increasing number of cigarette years. Additional adjustment for other risk factors (triglyceride, uric acid, body mass index, alcohol use and hypertension) also showed a strong independent contribution of smoking to GS, ASL and ASA. We concluded that the cumulative exposure to cigarette smoking was an independent indicator of the severity of coronary atherosclerosis as well as thoracic aortic atherosclerosis.