Aims To determine the reliability and validity of the Severity of Dependence Scale (SDS) for detecting cannabis dependence in a large sample of in-patients with a schizophrenia spectrum disorder. Design Cross-sectional study. Participants Participants were 153 in-patients with a schizophrenia spectrum disorder in Brisbane, Australia. Measurements Participants were administered the SDS for cannabis dependence in the past 12 months. The presence of Diagnostic and Statistical Manual Version-IV (DSM-IV) cannabis dependence in the previous 12 months was assessed using the Comprehensive International Diagnostic Interview (CIDI). Findings The SDS had high levels of internal consistency and strong construct and concurrent validity. Individuals with a score of =2 on the SDS were nearly 30 times more likely to have DSM-IV cannabis dependence. The SDS was the strongest predictor of DSM-IV cannabis dependence after controlling for other predictor variables. Conclusions The SDS is a brief, valid and reliable screen for cannabis dependence among people with psychosis.