Purpose: To investigate the usefulness of the Canadian Occupational Performance Measure (COPM) in a day treatment programme for clients with rheumatoid arthritis.Method: The study was conducted in two parts. In the first part rehabilitation without changes in the programme was performed (n = 16). After that the COPM was introduced to all team members. In part two the COPM was used (n = 40). Clients' experiences of participation in the process were studied via a structured interview 2 - 4 weeks after discharge in both parts. Qualitative interviews were conducted with team members before part one and after completion of part two.Results: Staff expressed that the COPM improved client participation in the rehabilitation process. Goals were formulated distinctly, and focused on activity and performance rather than function. Team conferences were focused on the client's needs. Outcome was considered clear and evident to the client. The changes in client routines demands thorough introduction, support and involvement, and takes time. Involvement and motivation for changing practice were difficult to obtain, this could be a result of a large staff turnover during the data collection period.Conclusions: The COPM should be seen as an aid to ensuring client participation in the goal formulation process, and facilitating treatment planning and evaluation of outcome.