Objective: In this study we aimed to examine the angiographic findings, traditional risk factors and natural history of Turkish patients <40 and ≥40 years old with coronary heart disease (CHD). Materials and Methods: The records of 491 patients with stable angina pectoris or acute coronary syndrome (ACS), who had undergone coronary angiography (CAG) were reviewed. The patients <40 years (group 1) and ≥40 years (group 2) were compared. Results: The study population was classified as group 1 with 240 patients (mean age 35.7±3.4 years) and group 2 with 251 patients (mean age 61.0±9.7 years). Smoking, family history, hypercholesterolemia, hypertriglyceridemia and low levels of high-density lipoprotein cholesterol were more prevalent in group 1 while diabetes mellitus, hypertension was higher in group 2. The common presentation among <40 years patients was ACS whereas stable angina was the most common presentation in patients ≥40 years old. Patients in group 1 showed a preponderance of single-vessel disease whereas patients of group 2 showed dominance of multivessel disease. Early clinical course of patients with ACS in group 1 was better than in group 2. Conclusion: Our study shows a significantly different clinical, angiographic and biochemical profile in <40 years patients with CHD compared with ≥40 years patients. Dominance of smoking and dyslipidemias that are the preventable risk factors in premature CHD patients is an important threat for our community health. Healthy life styles should be encouraged beginning from young ages and new precautions about smoking must be taken.