The purpose of this study was the development of a short self-reporting and supervisor-reporting questionnaire to assess generic work behavior of people with severe mental illnesses participating in psychiatric vocational rehabilitation. An 18-item generic work behavior questionnaire (GWBQ) was developed, which contains core dimensions derived from both supervisor scores and self-report scores. The factor structure of the GWBQ was replicated for both versions (supervisor and self reports). The GWBQ was very reliable for supervisor reports and moderately so for self-reports. Although self-report scores and supervisor scores correlated significantly, participants rated their own work behavior consistently higher than supervisors did.