The hands and knees of 150 patients who had undergone unilateral meniscectomy 19 or more (mean 24 . 7) years before were examined for evidence of osteoarthritis (OA). 65 had X-ray changes in the hands consistent with primary generalised OA. These patients showed more frequent and more severe knee OA, judged clinically and radiologically, in both unoperated and operated knees, than did the 85 patients without hand OA. The increased frequency in operated knees was independent of sex and age variables between the groups and remained significant after exclusion of patients with OA on the unoperated side. This study demonstrated that predisposition to "primary" OA influences the development and severity of "secondary" OA. It invalidates clear distinction between these subsets and emphasises the multifactorial nature of the disease.