It has been known that the obesity is one of the predisposing factors of the primary degenerative arthritis of knee. And nowadays, it seems that the number of obese person increases gradually in Korea. The authors studied 50 cases of the degenerative arthritis of knee clinically and statistically, compared with 50 cases of the control group, in the Department of Orthopedic Surgery, Seoul National University Hoispital from Jan. to Aug. 1981. The results were as follows: l. Among the degenerative arthritis of knee, the ratio of male: female was 1:9, and the age group with the highest frequency was the 5th. decade (48%). 2. Thirty-two cases (64%) was obese in the degenerative arthritis group, and 7 cases (14%) was obese in the control group. 3. The incidence of obesity in the degenerative arthritis group was 13.5 times higher than that in the control group, and it was highly significant statistically.