To assess the extent to which house officers know the social histories of their hospital patients, and to examine the factors that influence social history knowledge. In October-November 1992, all 31 internal medicine housestaff rotating on the hospital inpatient services at the University of Kentucky A. B. Chandler Medical Center completed questionnaires regarding the social histories of up to three of their patients. Responses were analyzed using simultaneous multiple linear regression analysis. Standard questions about social history were answered correctly only 29% of the time (two of seven items). The overall knowledge of patients' social histories was significantly less for supervising residents than for interns (p = .03) and, independently, for housestaff with greater patient loads (p = .04). Knowledge of a patient's social history was not related to the particular inpatient service, time the patient was admitted, or other characteristics of the patients or residents. The internal medicine residents' knowledge of their hospital patients' social histories was limited, particularly when the residents had relatively heavy patient loads or supervisory roles in patient care. The data suggest that patients' social histories may have been underemphasized during the residents' training.