OBJECTIVE: In patients with osteoarthritis (OA), moderate physical activity (PA) can reduce the progress of joint damage. PA is therefore an important target of in the non-surgical treatment of OA. To know about factors associated with PA can increase the success of interventions aiming at increasing PA. The aim of the study was to determine predictors of PA in patients suffering from OA to the hip or to the knee. METHODS: In total, 1250 outpatients from 75 general practices were consecutively approached, 1021 returned questionnaires containing sociodemographic data, and short forms of the International Physical Activity Questionnaire (IPAQ), the Arthritis Impact Measurement Scale and the Patient Health Questionnaire to assess concomitant depression. A hierarchical stepwise multiple linear regression analysis with the IPAQ continuous score as dependent variable was performed. RESULTS: Comparison of our findings with General population suggests that the overall PA of OA patients is decreased. Main predictors of PA were physical limitation to the lower body (beta = -0.179; P = 0.001), social contacts (P = -0.134; P < 0.001), pain (beta =-0.120; P = 0.001), age (beta = -0.110; P = 0.004) and the body mass index (beta =-0.043; P < 0.001). CONCLUSION: The findings emphasize the influence of physical as well as psychosocial factors on PA of patients with OA and should help to tailor future interventions more appropriately. Further research is needed to determine if these tailored interventions will result in better compliance and in increased PA.