This research assessed the body mass index of in school adolescents in Calabar municipality Local Government Area of cross River State, Nigeria. A total of 454 adolescents (10-19 years) consisting of 218 males and 236 females were randomly selected from 7 study schools in the Local Government Area. A semi-structured questionnaire was used to collect data on background information of the adolescents concerning the topic. Anthropometric measurements (weight and height) of the adolescents were obtained, and used to calculate the Body Mass Index (BMI).