Purpose Sickness absence and work disability can be a major burden for society and for both employees and self-employed workers. Validated tools for assessing the psychosocial risk factors of long-term disability, for matching effective interventions and for deciding when to resume work can be of great value. However, no validated tools exist for self-employed workers. The purpose of this study is to adjust and to validate the Work and Wellbeing Inventory (WBI) for entrepreneurs. Methods The sample consisted of 676 self-employed workers with a private disability insurance policy. Three groups were distinguished: business owners, liberal professions and doctors and paramedics. Reliability, construct validity and concurrent validity of the WBI were examined. Scale scores were calculated for each group of self-employed workers and compared with the scores of a representative group of 912 Dutch employees to test the adequacy of the existing (employee) test norms. Results The WBI for the self-employed showed good to excellent reliability figures. The construct validity and the concurrent validity of the WBI could be confirmed. Overall, the self-employed scored higher on job satisfaction, social support at work and perfectionism (diligence) and had fewer mental health problems compared to employees. Self-employed workers should not be treated as one group, as there were important differences between entrepreneurs, liberal professions and doctors and paramedics. Conclusions The reliability and validity of the WBI were confirmed. Important differences in the scores of employees and the self-employed were revealed. In addition, the group of self-employed workers appeared to be rather heterogeneous.