Introduction: The present study aimed to explain the effects of early childhood experiences of patients with obsessive-compulsive disorder by comparing attachment styles and defensive mechanisms in these patients with normal individuals. Method: A causal comparative research design was used. The statistical universe of the present study comprised all women suffer from obsessive-compulsive disorder residing in Yazd who sought treatment at Bahman Hospital during the first three months of 1385. The study sample included all those women approached the hospital on Saturdays, Mondays, and Wednesdays and diagnosed having obsessive-compulsive disorder by psychiatrist. The comparison group composed of 80 women from the normal population, who were possibly matched on age and educational status with the clinical group. To assess attachment styles and defensive mechanisms, the standardized Persian version of the adult attachment interview (AAI) and defensive mechanisms questionnaire were used, by order. Data were analyzed using descriptive indices and means were compared using T-test for independent groups. Results: Avoidant and ambivalent attachment styles were statistically greater among individuals with obsessive-compulsive disorder than normal controls. Normals tended to employ more mature defensive mechanisms than their obsessed counterparts. Conclusion: First, parental overprotection and unresponsiveness are associated with obsessive-compulsive symptoms. Second, treatment of obsessive-compulsive disorder is accompanied by a significant increase in the use of mature defensive mechanisms.