Background and Objectives: Fibromyalgia syndrome (FMS) is defined as a chronic pain syndrome that is characterized by widespread pain, tenderness, and diffuse stiffness. In addition, neuropsychological symptoms such as fatigue, sleep disorders, poor mood, cognitive impairment, and headaches are often reported. Many reports have addressed the coexistence of affective disorders and anxiety with FMS, yet few have focused on its association with obsessive compulsive disorder (OCD). We investigated the occurrence of classical patterns of OCD in participants with FMS and assessed their effect on pain perception and functional impairment. Material and Methods: The research population included 37 patients diagnosed with FMS, treated at the Rheumatology Clinic in the Sheba Medical Center, Tel-Hashomer, Israel. We used validated questionnaires including a demographic questionnaire, a questionnaire on average and maximal pain intensity, the Eysenck Personality Questionnaire-Revised (EPQ-R), the Perceived Stress Scale, the Pain Catastrophizing Scale, the Pain Obsessive questionnaire, and the Yale–Brown Obsessive Compulsive Scale (Y-BOCS). Results: Patients with FMS were found to have intrusive and obsessive thoughts regarding pain for several hours every day, causing a high degree of anxiety and high levels of pain, catastrophizing, and magnification, leading to helplessness and functional impairment. In total, 27% of the patients reported severe malfunction due to pain and pain ideation, and 49% demonstrated mild obsessive compulsive symptoms that were strongly correlated with pain intensity and functional impairment. Conclusions: Obsessive compulsive thinking patterns contribute to pain magnification and to the cognitive aspects of fibromyalgia syndrome. [ABSTRACT FROM AUTHOR]