Presenting Author details:joselito600@yahoo.es La Fuente s/n, 31003 Burlada (Navarra), Spain, Tel.: +34 656740772. Background: Cannabis abuse is thought to increase the risk of developing schizophrenia. However several studies have examined the influence of current cannabis abuse on illness characteristics, little is known about the antecedents of pre-psychotic cannabis abuse in patients with psychosis and its effects on the clinical picture of the subsequent illness. In this study we aimed to examine in a sample of patients already diagnosed with a psychotic disorder, the predictors and consequences of: (1) pre-psychotic cannabis abuse, (2) early cannabis abuse and (3) current cannabis abuse. Methods: Pre-psychotic characteristics included sociodemographic variables, childhood and adolescence adjustment. Phenotypic measures included age of illness onset, psychopathology (OPCRIT) and a short neuropsychological battery. These characteristics were then compared according to patients' pre-psychotic and current history of cannabis abuse. Results: A sample of 337 patients with psychosis was included. It was found that pre-psychotic cannabis abuse was associated with better social but worse school premorbid adjustment. Early cannabis abuse predicted an earlier age of illness onset and more negative and cognitive symptoms. Finally, current cannabis abuse was associated with more severe positive, manic and depressive symptoms. Conclusions: While psychotic patients who comorbidly abuse cannabis may have more prominent positive and affective symptoms, those who started abusing cannabis during their early adolescence have poor adolescent school adjustment, early onset of illness and more prominent negative symptoms and cognitive abnormalities.