In an acute care hospital, a major performance indicator is patient length of stay. This study, in a large university teaching acute care hospital in Canada, examined the effect of psychosocial problems on length of stay, controlling for patient demographics and medical condition. Average days stay for Diagnostic Related Groups (DRGs) was used as a proxy variable for severity of medical condition, and the Person-in-Environment (PIE) classification system was used to measure psychosocial problems. Data were collected on a sample of 160 patients; 78 in psychiatry and 82 in medical/surgical wards. In a regression analysis, the severity of the patient's psychosocial problem was a more significant predictor of length of stay than the DRG variable. The identification of psychosocial problems and their severity add an important and complementary dimension to research into the effectiveness of social workers in reducing length of stay. Workers found clients had significantly more problems related to their social role functioning than problems in the environment.