2,063 adult people of a Beijing suburban village were surveyed for osteoarthritis of the knees. Questionnaire was completed in all. 799 (38.7%) responded to have knee joint pain. 311 with knee joint pain and 212 without knee joint pain were selected randomly for X-ray films of the knees. In the former group, 79 showed osteoarthritic X-ray changes and were thus diagnosed as such, accounting 24.7% of those with knee pain. In the latter group, all were not diagnosed as clinical osteoarthritis, yet 54 (25.5%) showed also X-ray osteoarthritic changes. In both groups the X-ray osteoarthritic changes increased in parallel with increase of age, reaching 78% in those aged 60 and more in the former group and 67% in the latter group. 100 retired cadres were similarly surveyed but all had X-ray films of the knees taken. 51 of 100 responded knee pain, out of whom 49 (95.9%) showed X-ray osteoarthritic changes and were thus diagnosed as such. The overall prevalence rate of osteoarthritis of knee in rural population as judged by the 523 who had taken X-ray films (people with and without knee pain are not entirely proportional) is about 9.6% and that of 100 aged retired cadres is 49%. Those with X-ray knee osteoarthritic changes but without knee pain were not categorized as clinical osteoarthritic cases.