Cognitive impairments are among the most debilitating symptoms of mental illness and most highly predictive of functional outcomes. Cannabis intoxication impairs cognitive processes and there is increasing evidence for longer lasting impairment with long-term or heavy cannabis use. Cognitive dysfunction associated with chronic cannabis use is similar in many respects to the cognitive endophenotypes that have recently been proposed as vulnerability markers of schizophrenia. The prevalence of cannabis use among people with psychotic disorders, the potential for cannabis to trigger psychotic symptoms and episodes, and the neurobiological interactions between the endogenous cannabinoid system and the pathology associated with psychosis indicate a need to further investigate the nature and mechanisms of cognitive impairments associated with cannabis use. The endogenous can-nabinoid system plays a significant role in attention, learning and memory in particular, and in mediating inhibitory and excitatory regulatory mechanisms in the brain. There is evidence that the endocannabinoid system is altered in schizophrenia and accumulating evidence of disturbances in the system associated with exposure to cannabis or cannabinoids. This presentation will summarize what is known about the longterm cognitive effects of cannabis, describing some of the most recent research and its relevance to psychotic disorders.