A total of 39 schizophrenic patients with a history of current cannabis abuse at index admission was compared with a control group of schizophrenics without substance abuse matched for age, gender, and year of admission. At follow-up after 68.7+/-28.3 months, 27/ 39 cases and 26/39 controls could be investigated. 8/27 cases (30%) had continued cannabis abuse, 6/27 (22%) had become alcohol abusers. Only one patient of the control group had started abusing alcohol. Patients with previous cannabis abuse had significantly more rehospitalizations, tended to worse psychosocial functioning, and scored significantly higher on the psychopathological syndromes "thought disturbance" (BPRS) and "hostility" (AMDP). These results confirm the major impact of cannabis abuse on the long-term outcome of schizophrenic patients.