Obesity among adolescents is increasing in both developed and developing countries. However, previous studies have paid little attention to the roles that gender and body weight variables play in health-related behavior. This article examines the effects of these two variables on health-related behavior in Taiwanese adolescents. A cross-sectional descriptive design was used with three body weight categories (underweight, average and overweight) and two gender categories (female and male). Data were analyzed using descriptive statistics, Student's t test, and one-way ANOVA with Scheffe's post hoc test. The results showed that average weight adolescents scored significantly higher than their overweight peers in the three dimensions of social support, health responsibility, and exercise behavior. Average weight adolescents also scored higher than the underweight group in the dimension of health responsibility. Girls scored significantly better than boys in five out of the total six health-related behavior - scoring lower only in the exercise dimension. These findings should sound an alarm for all public health professionals to take heed to what is happening to our youth. School and family health promotion counseling should be encouraged for overweight adolescents to improve their exercise and lifestyle habits. Based on the findings, school health promotion programs should focus on gender differences. Girls, in particular, need encouragement to improve their exercise habits.