The association between obesity and osteoarthritis (OA), was studied by analysis of data from an epidemiologic survey of a population of 1071 men and 1097 women in The Netherlands. A total of 20 joints and groups of joints were investigated. OA was clearly associated with obesity in the most frequently affected joints, weight bearing as well as nonweight bearing. This association was less strong for severely affected joints than for mildly affected joints. This pattern was neither compatible with a generalized (metabolic) abnormality nor with weight induced mechanical "wear-and-tear". OA is a heterogeneous condition and some site specific associations with obesity are strong, thus there is scope for prevention by weight reduction for some sites.