A retrospective investigation of case-notes compared 54 incidents of informal psychiatric in-patients being detained in hospital on an emergency basis with 66 incidents of discharge against medical advice (AMA). The characteristics of the two groups were compared. Detained patients were more likely to have been detained previously, to be suffering from a psychotic illness, and to have threats of violence or self-harm mentioned in their case-notes. AMA patients were more likely to have a history of substance abuse but were no more likely than the detained group to have been discharged AMA in the past. The results suggest that psychiatrists in this hospital are using current legislation on detention appropriately.