The purpose of this study was to report on the estimates and distribution of body mass index in a sample of Malaysian adolescents. The study utilized a cross-sectional design and multi-stage random sampling of secondary schools to select 5 urban and 9 rural schools in Kedah and Penang. A total of 6555 male and female adolescents (11-15 years old) of Malay, Chinese and Indian ethnic groups were measured for weights and heights for body mass index calculation. Information on household demographic and socioeconomic were obtained from parents through self-administered questionnaires. Analyses of body mass index distribution by location, ethnicity, gender and age were conducted using Chi-square test of SPSS 11.5. More of the rural (12.1%) and urban (19.4%) adolescents were underweight and overweight, respectively. While in all ethnic, gender and age groups, rural adolescents were more likely to be underweight, more of the urban adolescents were overweight. The prevalence of underweight was highest among the Indians (19.2%) and lowest in Chinese (7.2%). The prevalence of overweight in the three ethnic groups was in the range of 18-19%. More male than female adolescents were underweight (15% vs 7.8%) and overweight (19.5% vs 16.7%). Consistent patterns were also observed across location, ethnic and age groups. As age increased, the prevalence of overweight decreased across the ethnic and gender groups. The reported findings can serve as current reference on body mass index distribution of Malaysian adolescents and a basis for future efforts in health and nutrition interventions for Malaysian children and adolescents.