Aim of the study: this study aimed to study the prevalence and phenomenology of OCS in a sample of Egyptian patients as well as in a matched control group. Subjects and Methods: 372 patients and 308 controls matched for age, gender, religion, and years of education. We used ICD (10) Research criteria for diagnosing the different psychiatric disorders. OCS prevalence and symptomatology were assessed by Y-BOC checklist. The Obsession section of PSE (10th) version used to differentiate between OCS and OCT in order to make our results as valid as possible. Results: A significant prevalence of OCS in the clinical psychiatric population (62.1%) than in the general population (38%). We found a difference between results obtained by Y-BOC checklist (62.4% in clinical population versus 38% in the general population) and PSE (31.2% in the clinical population versus 21.4% in the general population), Conclusions: (1)OCS are highly prevalent in normal and psychiatric population and they related to OCD in nature of symptoms but differ in intensity, quality and content. This conclusion needs validation by further psychosociobiological studies. (2) Psychiatric disorder affects the form, content but not the nature of comorbid OCS.. (3) It is very important to delineate the similarities and differences among the different nosologies of obsessive compulsive phenomen(4) the genesis of OCS in clinical psychiatric population is differ from that in general population. (5) OCS found in clinical psychiatric population are pathological symptoms