The issue, whether the use of cannabis contains a higher risk to develop psychotic disorders, is disputed since the 1930s. Two questions are of central concern: Firstly, if the use of cannabis is causal for the development of psychotic disorders, and secondly, what the neurobiological connection consists of. In this review we give an overview on epidemiological studies concerning the issue and on neurobiological studies on the effects of cannabis in the brain. On the basis of cohort studies that have been conducted within the last decades and recent meta-analyses the hypothesized connection between cannabis use und psychotic disorders can be corroborated. The risk to develop psychotic symptoms and also schizophrenic psychoses is thus explicitly elevated for young people who use cannabis. Cannabis use can be considered a component cause, a dose dependency exists. An information of the public concerning this matter is required in order to prevent a rising incidence of psychotic disorders in times of an increasing ease of handling of cannabis.