Objectives: The study was designed to examine the impact of the comorbidity of personality disorders with the obsessive-compulsive disorder on the medical treatment of patients suffering from both. Method: Following a quasi-experimental design, 30 subjects suffering from obsessive-compulsive disorder were selected through convenient sampling, 15 with personality disorders and 15 without, They were treated with Fluoxetine for 3 months. The research tools comprised a demographic questionnaire, Hamilton Depression Scale, Yale-Brown Obsessive-Compulsive Scale, and the MCMI-f1. The subjects were homogeneous in terms of other variables affecting treatment, such as sex, age, and duration of the disorder. The data was analyzed by t-test and chi2 statistical methods. Results: The results demonstrated that: a) there was no significant difference in the severity of post-treatment obsession among the two groups, and that medical treatment significantly reduced obsession in both groups b) there was no significant difference in the severity of pre-treatment obsession among the two groups.