Objective. To investigate the prevalence of betel nut chewing and related factors among adolescent students in general, manufacturing, commercial, agricultural and medical. technology schools in Taiwan. To make suggestions regarding how health authorities can reduce the number of students taking up the habit. Materials and methods. A cross-sectional survey was designed, and 10,288 students answered the questionnaire. Results. Significantly more mate than female students were betel nut chewers. The Less urbanized areas were also associated with a higher prevalence of the habit. The prevalence of the habit grew with increasing age. By analysing betel nut chewing behaviour, it was found that most students started chewing betel nuts because of curiosity, and most obtained betel nuts from their friends and classmates. Betel nut chewing behaviour is definitely related to peer pressure. Most betel nut chewers did not realize that withdrawal could lead to physiological reactions, and they were ignorant of any risk to health even though they were compulsive betel nut chewers. The health-harming behaviours of both smoking and drinking were found in many betel, nut chewers, particularly smoking. Conclusion. This study confirmed the need for a health education programme dealing with the health risks of betel nut chewing for students at risk. The health authorities could also develop a programme for betel nut chewing among Taiwan's adolescent students, emphasizing the dangers of this habit. (C) 2003 The Royal. Institute of Public Health. Published by Elsevier Ltd. All rights reserved.