Objectives: In Korea, among CAD patients, M(male) to F(female) ratio is 2.33 : 1, but below the age of 50 years, M : F ratio is 6.95 : 1.We tried to find what are the major contributing factors for this large differences between sexes in the prevalence of CAD in young Korean patients with CAD. Results: Nineteen % of the male patients were below 50 years of age and 6.8 % of the female patients were below 50 years (p<0.001) of age. In the smoking CAD patients, a large difference of prevalence of CAD was noted between different sexes below age of 50. But in the nonsmoking CAD patients, the differences of prevalence of CAD between different sexes became very much narrowed in age of below 50. The presence of other major risk factors did not narrow the differences of prevalence of CAD between sexes in young ages. The distribution of the prevalence of CAD showed a shift of the prevalence to the younger ages in male CAD patients and shift of the prevalence to older ages in the female CAD patients. This phenomenon was more prominent in the CAD patients with risk factors of smoking, hypertension, or hyperlipidemia. Conclusion: Smoking is one of the major contributing factors to the much higher prevalence of CAD in young male Korean patients (below age of 50 years) compared with female patients. Table 1. Distribution of CAD patients.