Social work is a common service in medical rehabilitation in Germany. However, studies show inconsistent effects of social work interventions. This study aims to compare a self-reported rehabilitation outcome, which covered all functioning domains of the International Classification of Functioning, Disability and Health, in patients with and without social work interventions. The analysis is based on administrative data comprising individuals admitted to medical rehabilitation services due to an orthopedic ( n = 54,056) or cardiac ( n = 16,955) diagnosis between 2007 and 2011. The intervention and control groups were matched by propensity scores (PS) controlling for sociodemographic, clinical, and sociomedical characteristics. A sufficient overlap of the PS allowed a successful matching in both samples. Orthopedic and cardiac patients receiving social work interventions had a worse outcome compared to the control group ( d = −.20, p = .000). The results indicate a clear-cut need for in-depth analysis of social work practice in medical rehabilitation and implementation of controlled studies.