A cardiovascular epidemiologic survey was performed in three areas (Sakuto-cho, Sanyo-cho and Osafune-cho) of Okayama prefecture in 1981 to determine age and sex differences in serum HDL-and total-cholesterol. A total of 1077 subjects, 389 male and 688 female, with 412 under 60 years of age (younger group) and 655 over 60 years of age (elder group) were studied, and the following results were obtained. The ratio of HDL-cholesterol to total-cholesterol in subjects from the mountain town of Sakutocho was higher than in those from urban areas (Sanyo-cho and Osafune-cho). In the female group, HDL-and total-cholesterol values were higher and the HDL-/total-cholesterol ratio lower than in the male group. Among healthy individuals, the value of HDL-cholesterol was higher in the younger and female groups. However, in the female group, the total-cholesterol value was also high, so there was no significant difference between sex concerning the HDL-cholesterol to total-cholesterol ratio. In those with hypertension, ECG abnormalities and obesity, we found a higher total cholesterol level and lower HDL-cholesterol to total-cholesterol ratio than in the healthy subjects. This tendency was especially remarkable in the elder group. We found no differences in the HDL cholesterol values according to sex and age. However there was lower HDL-cholesterol to total-cholesterol ratio in the female group than in the male group resulting from a higher total-cholesterol value in the former.