Study objective-The aim was to investigate risk factors for cancer of the buccal and labial mucosa in Kerala, southern India.Design-The investigation was a casecontrol study.Setting-Regional Cancer Centre, Trivandrum, Kerala, and local teaching hospitals.Participants-Cases were all those registered with oral cancers at the Regional Cancer Centre during 1983 and 1984 (n = 414). Controls (n = 895) were selected from admissions to the cancer centre who were found to have non-malignant conditions, or from patients attending outpatients in teaching hospitals of Trivandrum medical college with nonmalignant conditions.Measurements and main results-The risk in males of the following habits was investigated: pan (betel)-tobacco chewing, bidi and cigarette smoking, drinking alcohol, and taking snuff. Only pan-tobacco chewing was investigated in females as very few indulged in other habits. Among males predisposing effects were found for pantobacco chewing (p < 0-001), bidi smoking (p < 0001), drinking alcohol (p < 0-001), and taking snuff (p < 0-01). As in males, pantobacco chewing also had a predisposing effect in females (p < 0-001). Duration of use was a better predictor of risk than either daily frequency of use or total lifetime exposure, both for pan-tobacco chewing (especially if the habit started before age 21 years) and bidi smoking. However, there were also very high risks associated with the current occasional use of both factors. Pan