• To evaluate the clinical effectiveness of short-term (threemonth maximum length of stay) and long-term (discharge based on clinical judgment) hospitalization, the inhospital course of 68 "short-" and 58 "long-term" psychiatric patients was studied. The results indicate that patients assigned without bias to shortterm treatment improved to a significantly greater extent in affective and cognitive disturbance when compared to patients assigned to long-term treatment. Exploration of differential treatment patterns, however, indicated that these results could be entirely accounted for by the significantly greater use of group therapy as an additional treatment modality in the short-term units. The need for a more systematic exploration of the effect of restricted hospital stay on the treatment patterns of the clinician and the effect of these differential treatment patterns on inhospital improvement is emphasized. The necessity for follow-up data to gain a complete picture of these treatment contrasts is clear.