Background: Oral Submucous Fibrosis (OSMF) is premalignant condition having high malignant transformation rate and increased risk of oral squamous cell carcinoma which itself accounts for 40% deaths due to malignancy across the world. Objective: To study the prevalence of OSMF among betel nut chewers in north Indian population. Methods: A total of 320 subjects consisting of 246 males and 74 females Dental patients of Patna were selected. The subjects were divided into two groups. The first group was control group consisting of 160 subjects including 123 males and 37 females who didn__ampersandsign#39;t had the habit of betel nut chewing. Another group included betel nut chewers with same no of subjects as that of control group. All participants were screened for presence of OSMF by first 2 authors independently according to the WHO prescribed coloured atlas, clinical examination and history. Results: Prevalence of OSMF was 75% among betel nut chewers. Males were more affected (70%) than the females. The maximum no of cases reported were in the age group of 30-40 years. Conclusion: Betel nut chewing can be considered to be a harmful habit and necessary public health measures should be taken to eradicate this habit.