Eleven patients with a psychosis in connection with cannabis abuse admitted to two mental hospitals during 1 year were examined. Patients with a pre-existent psychosis or a mixed abuse were excluded. The patients were divided into three groups: acute, subacute and chronic. The features of the disease were essentially similar in all patients, with a mixture of affective and schizophrenia-like symptoms, confusion and a pronounced aggressiveness. The course as a rule was self-limiting leaving no residual symptoms. There was almost no heredity of severe mental disease. The symptoms were very similar to those seen in cycloid psychosis, and a possible relationship between the two diseases is discussed. As regards the widespread abuse of cannabis we conclude that psychosis is a rare complication but that in unclear psychotic states it is recommended to actively search for a cannabis psychosis.