Objective of this study is to evaluate the selection of patients to be admitted to a hospital medical short-stay unit (SSU) where acute medical admissions with a predicted length of stay of between 24 and 72 h are managed. This is a retrospective observational study evaluating outcomes of all admissions to the medical SSU between January 2005 and December 2008. Factors that influence inappropriate allocation of patients to the SSU or alternative longer stay medical units were evaluated. Length of stay (LOS), mortality, Charlson score, admission to intensive care unit (ICU) (from the SSU), discharge diagnosis, and 7-day readmission rate were analysed. Over 4 years, 45% of the general medical inpatient take, 9,125 admission episodes, were managed by the medical SSU. On an average, 72% of these admissions to the SSU stayed fewer than 72 h. After excluding in-hospital deaths, there were 8,381 admissions to the general medical unit discharged within 72 h, and 77% of these were managed by the SSU during the study period. Inappropriate admissions to the SSU (LOS more than 72 h) tended to be older patients with more complex medical comorbidities. Other factors contributing to prolonged stay in the SSU included weekend admissions, and transfers to the ICU. The 7-day readmission rate was low at 3%; the all-cause hospital mortality for patients admitted to the medical SSU was 2% despite a 32% increase in workload in the medical SSU over these 4 years. In the context of fixed resources and a steeply increasing patient workload, a large proportion of general medical patients can be managed in a medical SSU with the majority being discharged home within 72 h while keeping all-cause in-hospital mortality and readmission rates low. More accurate identification of appropriate patients on admission by using a physiological clinical score and addressing operational issues particularly on weekends could lead to a more efficient SSU.