The instrument Assessment of Work Performance (AWP 1.1) can be used to assess an individual's skills during work performance - how efficient and appropriate a client performs a work task. The instrument is currently used by over 300 assessors working in a variety of work rehabilitation settings in Sweden, and it has been used with over 10,000 clients. In this study, the construct validity of the AWP 1.1 was tested with 364 assessments of clients with a variety of various work-related problems assessed by six occupational therapists in a Social Insurance Office in Sweden between 2004 and 2005. Principal Component Analysis shows construct validity of the AWP 1.1. Further, the findings indicate that the instrument is sensitive and discriminates between clients, and no gender related patterns were identified.