Forty oral cancer patients identified consecutively in Changhua Christian Hospital between 1990 and 1992 were compared with 160 population-based controls, matched for sex, age, area of residence, and educational background. Betel quid chewing was positively associated with the risk of oral cancer with adjusted odds ratio of 58.4 (95% CI: 7.6-447.6). The greater the number of years of chewing betel quid, the higher the risk of oral cancer; the adjusted odds rations were 12.9, 93.7 and 397.5 for < 21, 21-40, and > 40 years of betel chewing as compared with the non-users. The risk also increased with the quantity chewed per day; the odds ratios for those chewing < 10, 10-20 and > 20 quids/day were 26.4, 51.2 and 275.6, respectively. These odds ratio estimates were all statistically significantly different from the null value of unity.