In order to clarify the significance of obesity in atherosclerotic risk at different ages, the relationship between the body-mass index, serum sialic acid concentration, and various atherosclerotic risk factors were investigated for healthy subjects in three different age groups, 35-39, 40-49 and 50-59 years old. The body-mass index correlated significantly with mean arterial blood pressure, fasting blood sugar, serum triglycerides, atherogenic index and serum uric acid in all age groups. The magnitudes of the association of body-mass index with mean arterial blood pressure, fasting blood sugar and serum triglycerides decreased with age, while those of the association with atherogenic index and serum uric acid were not different among the three age groups. Body-mass index did not show significant correlation with white blood cell count, platelet count or smoking in any of the age groups. Simple and multiple regression analyses showed that body-mass index was significantly correlated with serum sialic acid in the 35-39-year-old group, but not in the other two groups. Neither the percentage of obese subjects (body-mass index > 26.4) nor the mean values of body-mass index were different among the three groups. These results suggest that for younger people, the body-mass index is related more closely with some atherosclerotic risk factors (e.g. blood pressure, blood sugar and serum triglycerides), and obesity may be possibly more involved in the progression of atherosclerosis, compared to more elderly people.