The prevalence and related risk factors of betel quid chewing among adolescent students were studied in a junior high school (group 1) and in a vocational school (group 2) in southern Taiwan. Group 1 consisted of 3548 participants (89.7% response rate) and group 2 of 1358 (97.6% response rate). The students were asked to complete a questionnaire anonymously. In the junior high school 1.9% of students including all grades (13-15 years old) and both sexes was found to be a current betel quid chewer and 14% was an ex-chewer, whereas 10.2% of vocational school students (16-18 years old) was a current chewer and 31% was an ex-chewer. The prevalence of betel chewing was significantly higher among boys than girls. A high proportion of chewers was also a smoker and alcohol drinker. A statistical analysis of sociodemographic factors showed that male students who smoked tobacco, consumed alcohol and were friends or classmates of students who were betel quid chewers, were the likeliest adolescents to chew betel quid.