Fifty patients satisfying DSM-III-R criteria for mania were included in a naturalistic study. Manic patients were categorized into three diagnostic groups according to the DSM-III-R criteria of non-psychotic or psychotic mania, and into the four groups obtained by the cluster analysis of Double (Double, D.B. (1991) Compr. Psychiatry 32, 187-194). Personal history and short-term outcome did not differ between the DSM-III-R diagnostic groups nor between the groups defined by cluster analysis, although non-psychotic manic patients more frequently tended to receive lithium and/or anticonvulsant drugs alone at discharge. Cluster 3 patients presenting with manic and 'schizophrenic' symptoms had an earlier age of onset and were younger at admission than patients in the other three clusters.