Relatively little is known about the prevalence of knee and hip osteoarthritis in the general population.To estimate the prevalence of knee and hip osteoarthritis and the appropriateness of joint replacement in a general population of older individuals, the validated Knee and Hip OsteoArthritis Screening Questionnaire (KHOA-SQ) was sent to a random sample of individuals aged 60 to 90 years, stratified by age and sex, living in a single province in Spain. Respondents positive for knee or hip osteoarthritis on the KHOA-SQ were invited to be examined by an orthopedic surgeon. Diagnosis of knee or hip osteoarthritis was based on clinical and radiographic data. For respondents judged as having osteoarthritis, the appropriateness of knee or hip replacement was evaluated using published explicit criteria.Of 11 002 individuals contacted, 7577 completed the KHOA-SQ. The derived prevalence of hip osteoarthritis was approximately 7.4%. It was slightly higher in women (8.0%) than in men (6.7%) and tended to increase with age. The estimated appropriateness rate for hip replacement was 37.7% in men and 52.7% in women with osteoarthritis. The derived prevalence of knee osteoarthritis was 12.2%; it was significantly higher in women (14.9%) than in men (8.7%) and tended to increase with age. The estimated appropriateness rate for knee replacement was 11.8% in men and 17.9% in women with osteoarthritis.Knee and hip osteoarthritis are highly prevalent diseases in the older population. The estimation of appropriateness for hip replacement seems to be significantly higher than that for knee replacement.