Oral sub mucous fibrosis (OSMF) is a chronic, insidious, disabling disease of oral mucosa, oropharynx, and rarely, the larynx affecting millions of people worldwide with a prevalence rate of 0.4 % in Indian rural population. It results in difficulty to open the mouth and can be disabling to the patient. The awareness of such a condition among oral physicians can help in timely diagnosis and thus appropriate treatment can be administered depending on the degree of involvement. Patients with OSMF need treatment for trismus correction, reconstructive surgery for any simultaneous oral malignancy. A case of oral sub mucous fibrosis occurring in a 35 year old male patient is presented with emphasis on the review of literature.