There is a high comorbidity between cannabis use and schizophrenia. Several factors contribute to this comorbidity: secondary development of addiction, cannabis-related induction of psychosis and shared neurobiological alterations. Meanwhile, there is evidence that cannabis use is associated with an increased risk of schizophrenia. Prospective epidemiological studies have shown that a frequent cannabis use doubles the risk for schizophrenia. Interestingly, schizophrenic patients with comorbid cannabis use often show significantly better performances in neuropsychological tests than patients without cannabis use. This is nevertheless not due to a positive effect of cannabis, but a sign of cannabis-related psychosis induction in subjects with a higher level of function and less cognitive impairment. Whether cannabis use leads to schizophrenia is determined by the individual vulnerability.