Oral submucous fibrosis (OSF), a premalignant and crippling condition of the oral mucous membrane, was studied to identify its relationship to various chewing and smoking habits. Two hundred and thirty-six consecutive cases of OSF were compared with 221 control subjects matched for age, sex and socio-economic conditions. It was found that chewing of areca nut/quid or pan masala (a commercial preparation of areca nuts, lime, catechu and undisclosed colouring, flavouring and sweetening agents) was directly related to OSF. Also, pan masala was chewed by a comparatively younger age group and was associated with OSF changes earlier than areca nut/quid chewing. However, chewing or smoking tobacco with various other chewing habits did not increase the risk of developing OSF. It was also found that frequency of chewing rather than the total duration of the habit was directly correlated to OSF.