The problem of substance abuse disorders in schizophrenia patients is reviewed, including the prevalence of co-morbid disorders, assessment, hypothesized mechanisms underlying abuse, and the clinical effects of abuse on the course of illness and cognitive functioning. The principles of treatment for dual-diagnosis schizophrenia patients are outlined, and the limitations of existing interventions are noted. Gaps in current knowledge about the impact of substance abuse on schizophrenia and its treatment are identified, and suggestions are made regarding promising avenues of research in this area.