Objective: To study the convergent and divergent validity of the Canadian Occupational Performance Measure (COPM). Design: Cross-sectional study. Setting: The occupational therapy departments of two university hospitals in Amsterdam. Subjects: One hundred and five consecutive outpatients. Outcome measures: The COPM is a measure of a client's self-perception of occupational performance in the areas of self-care, productivity and leisure. Outcome measures of the COPM are: the client's most important problems in occupational performance and a total score for performance and a total score for satisfaction for these problems. Problems reported in the COPM were compared with the Sickness Impact Profile (SIP68), the Disability and Impact Profile (DIP) and an open-ended question. Results: Complete data were obtained for 99 clients. The identification of occupational performance problems with the COPM surpassed the items reported in the SIP68, the DIP and the open-ended question, which confirms the surplus value of the COPM. Divergent validity was further demonstrated by the low correlation coefficients between the total SIP68 scores and the COPM. Seventy-four per cent of the occupational performance problems reported in the COPM had a corresponding item in the DIP and 49% had a corresponding item in the SIP68. Convergent validity was supported by the fact that 63% of the corresponding problems in the DIP were reported to be a disruption of quality of life and 74% of the corresponding problems in the SIP68 were identified as a disability. Conclusion: The results of this study provide supportive evidence for the convergent and divergent validity of the COPM. The data support the assumption that the COPM provides information that cannot be obtained with current standardized instruments to measure health.