The prevalence of substance abuse was investigated in 100 young chronic patients consecutively admitted to a long-term private psychiatric hospital. Data were obtainedfrom diagnostic research interviews with each subject at admission. Half of the subjects had concurrent diagnoses of psychiatric disor derandsubstance abuse. Onethird of the dual-diagnosis patients began using substances before the onset ofa diagnosable psychiatric disorder, and they more often bad a diagnosis of schizophrenia. Half of the dual-diagnosis patients abused three or more drugs. Implications of the findings for treatment and community management of dual-diagnosis patients are discussed.