The elderly frequently suffer long lengths of hospital stay (LOS). These long stays are often associated with long social care stays which occur when patients no longer require acute care and are awaiting post-discharge services. In this study, actual acute care LOS and social care LOS were studied specifically in hospitalized frail elderly. Our data demonstrate that frail elderly receiving only acute care do not suffer markedly prolonged total LOS (TLOS). However, in hospitalized frail elderly patients who experience acute care and social care stays, social care LOS accounts for over half of all hospital days. When patients were grouped and studied according to the type of post-discharge services being sought by the health care team, significant differences in acute LOS and social care LOS were noted. Subgroups of patients were also identified among the various groups which differed significantly in their LOS parameters. Patients who required more than one discharge plan during the course of hospitalization experienced the longest hospital stays of all groups, and spent almost 70% of these days receiving non-acute social care. In a study of the relationship between the intensity of social work intervention and social care LOS in the frail elderly, a statistically significant relationship was noted between the timing and frequency of social work intervention and the actual length of social care stays. Early and frequent social work interventions were associated with significantly shorter social care LOS. We conclude that the study of TLOS should include acute LOS and social care LOS to obtain a reliable measure of the course and cost of hospital care for the frail elderly. The study of social care subgroups may facilitate future investigations to define the social care problems which contribute most to TLOS, and the patient populations which should be most heavily targeted for early and intensive social work intervention.