Objective: The aim of this study was to determine the distribution of major risk factors among patients with atherosclerotic disease aged ≤50 years. Subjects and Methods: The study population comprised 944 patients aged ≤50 years with clinically significant manifestations of atherosclerotic disease compared with 350 consecutive (control) older patients (age >50 years). Results: The most significant risk factors for atherosclerotic disease of the supra-aortic branches were: smoking (87.5%, p < 0.001), family history of atherosclerosis (52.3%, p < 0.001), diabetes mellitus (28.5%) and being male (56.9%) (p < 0.05 for both). In patients with coronary artery disease, there was considerable disparity in the prevalence of smoking (85.4%), hyperlipoproteinemia (67.4%), and family history of atherosclerosis (68%) (p < 0.001). For peripheral artery disease, the most significant risk factors were smoking (97%, p < 0.001), hyperlipidemia (p < 0.01), and family history of atherosclerotic disease (p < 0.01). When compared to controls, patients with premature atherosclerosis smoked more frequently, had hyperlipidemia, had a family history of atherosclerosis, and were more frequently of male sex. Conclusion: Premature atherosclerosis was most frequently associated with smoking, hyperlipidemia, family history of atherosclerotic disease, and male sex.