Difficulties in the placement of two recurrently assaultive mentally retarded men who had been admitted to acute admission units for assessment led staff to hypothesize that mentally retarded patients were being inappropriately diverted into psychiatric services. To test this hypothesis, the charts of all mentally retarded patients admitted over two years were reviewed retrospectively. Contrary to expectations, there was no difference between the average length of stay of the mentally retarded patients and a comparison group of psychiatric patients. Furthermore, the mentally retarded patients presented with a full range of Axis I disorders, schizophrenia being the most common. It was concluded that, in general, the acute psychiatric services were being used appropriately for this group of mentally retarded patients.