The prevalence of modifiable cardiovascular risk factors (systemic hypertension, diabetes mellitus, cigarette smoking, low-density lipoprotein [LDL] cholesterol greater than or equal to 160 mg/dl and high-density lipoprotein [HDL] cholesterol less than 35 mg/dl) was determined in 321 men less than 60 years of age (mean +/- standard deviation 50 +/- 7) with premature coronary artery disease (CAD) documented at coronary angiography. The prevalence of these risk factors was markedly different than in the Framingham Offspring Study population, used here as a comparison group. In the patients with CAD, only 3% had no risk factor (other than male sex), compared with 31% in the Framingham Offspring Study subjects. Most patients with CAD (97%) had greater than or equal to 1 additional risk factor. When the patients with CAD were divided by age groups (40 to 49 years [n = 109], 50 to 59 [n = 191]), no significant differences were observed in the prevalence of risk factors between the young and older patients. The prevalence of systemic hypertension (41 vs 19%, p less than 0.001), diabetes mellitus (12 vs 1.1%, p less than 0.001), cigarette smoking (67 vs 28%, p less than 0.001) and HDL cholesterol less than 35 mg/dl (63 vs 19%, p less than 0.001) was markedly higher in the patients with CAD than in Framingham Offspring Study subjects, whereas the prevalence of LDL cholesterol greater than or equal to 160 mg/dl was not significantly different between patients with CAD and Framingham Offspring Study subjects (26 vs 26%).(ABSTRACT TRUNCATED AT 250 WORDS)