
Background: The causes of obsessive compulsive disorder (OCD) are yet unknown. Evidence of familial aggregation is one approach for investigating the role of genetics in the etiology of this condition. Objectives: To determine the rate of obsessive compulsive disorder (OCD) among first degree relatives (FDRs) of both probands &control group of a sample of psychiatric outpatients with OCD & their sociodemographic characteristics. Mathod: The study sample include 50 probands&312 of their relatives & compared with control group of 50 & 357 of their relatives, who were identified in psychiatric outpatient clinic & assesed by the use of semi-structured psychiatric interview schedule based on DSM IV criteria for diagnosis of OCD in addition, information were collected regarding sociodemograghic characteristics. Results: The prevalence of OCD was significantly higher in probands compared with control relatives (6.1% versus 2.5) (P<0.05). Females were affect more than males. Most patients were married, and of high education. Conclusion: The rate of OCD in FDRs is increased more than two & half fold than in the general population &this goes with that of other researches on this topic. this might suggest some genetic basis for OCD at least partially, however there may be some biological relationship.