Objective: The aim of our study is to examine the effects of the substance abuse on criminal and violent behaviors, clinical features of the disease in criminal male with schizophrenia. Methods: Male inpatients with schizophrenia diagnosed according to the DSM-IV criteria who had been hospitalized for observation or mandatory treatment in Bakirkoy Research and Training Hospital for Psychiatry, Neurology and Neurosurgery forensic psychiatry unit were participated in the study. Patients with substance use disorders according to the DSM-IV criteria at any time of their lifes and/or at that time were assessed, two groups as patients with substance use disorders (n=50) and patients without substance use disorders were compared using the questionnaire for demographic and clinical characteristics, Positive and Negative Syndrome Scale (PANNS), Schedule for Assessing the Three Components of Insight and Taylors Violence Rating Scale. Results: In our study 90% of the patients with substance abuse comorbidity were paranoid subtype. Total number of committed crimes was higher in patients with substance abuse comorbidity. Their crimes involved serious violence included homicide and attempted homicide. They committed crimes mostly against strangers using frequently knives and fire guns. Eighty-eight percent of the patients with substance abuse comorbidity stated that they used cannabinoid and several substances during these crimes. Their PANSS scores were higher. It had been found that they had experienced more physical violence at childhood, more suicidal attempts and self-injury behaviors. Conclusions: Substance abuse co-morbidity in schizophrenia markedly affects the psychopathology, violent behaviors, criminal behaviors and compliance with the treatment. Studies investigating the causal relationship between substance and crime in schizophrenia can be helpful in the development of methods targeting protection. [Anadolu Psikiyatri Derg 2015; 16(2.000): 104-112]