AbstractBackground and purpose: Obsessive-Compulsive Disorder (OCD) is a disease that appears to be under-diagnosed and under-treated despite the evidence for effective treatments. There are variable estimates of OCD prevalence (many studies reported that its prevalence is betwent 2% and 3% in general population). It is dependented to age, sex, marital status, socio-economic & educational state, in population.Materials and Methods: This method was a cross sectional descriptive study on high school girl students in Sari city. 3104 girls were selected and interviewed through randomized systematic & cluster sampling method from all high school girl students. The assessment was done by Muadsley obsession compulsive inventory & demographic inventory. After the data were analized by descriptive and qualitative methods.Results: 108 students were excluded then 2996 girls were entered in this study, 31.2% (936 individuals) had OCD and mean of their age was 16.22 ± 3.4. 30.7% of girls was first child, 35.1% of mothers & 34.7% of fathers had low educational class and low socio economic state.Conclusion: Prevalence of OCD in high school girl students was significant in sari city, and it was related to number of birth, family size, and low socio-economic and educational level.