Angiotensin-converting enzyme (ACE) is a key enzyme in the renin-angiotensin system. The wide distribution and multifunctional properties of these peptides suggest that ACE could be involved in various pathophysiological conditions. Recent evidence has shown that angiotensin converting enzyme (ACE) inhibitors possess cognition enhancing activity. For this reasons, we aimed to investigate whether ACE insertion/deletion (I/D) genetic variants are risk factor for schizophrenia. 238 patients with schizophrenia, 288 first-degree relatives of schizophrenic patients and 205 healthy controls were included in the study. Polymerase chain reaction analysis was used to detect the insertion/deletion (l/D) polymorphism of the ACE gene. The Statistical analysis were performed with the use of Pearson's chi-square test. The frequecy of the distribution of ID genotype was significantly overpresented in schizophrenic patients and their relatives compared to controls. In contrast, the frequency of II genotype was higher in controls than patients and relatives. The genotypes of ACE in patients with schizophrenia are not different from those of the relatives. Relatives might develop schizophrenia because of sharing same genetic with patients depending on environmental factors. It seems that ID genotype of ACE a risk factor for the development of schizophrenia.