Body composition but also physical activity patterns underlie gender typical differences throughout human life. In the present study the body composition of 354 girls and 280 boys ageing between 11 and 18 years originating from Eastern Austria were analyzed using bioelectrical impedance method. Normal weight according to body mass index categories was a strict inclusion criterion. Information regarding physical activity during school and leisure time, daily nutritional habits, subjective body satisfaction and weight control practices were collected by means of a structured and standardized questionnaire. Results of the analyses reveal that--as to be expected--adolescent boys and girls differed significantly in body composition, but also in physical activity patterns. Even normal weight girls exhibited a significantly higher amount of absolute and relative fat mass, whereas normal weight boys showed a significantly higher amount of fat free body mass. Furthermore male adolescents were significantly more physically active than their female counterparts. According to the results of multiple regression analyses physical activity patterns had beside sex an independent influence on body composition parameters during adolescence. In contrast, girls and boys showed only minor differences in nutritional habits and weight control practices. Nutritional habits, body satisfaction and weight control practices were not significantly related to body composition parameters. The observed gender differences in body composition as well as in physical activity patterns are interpreted in an evolutionary sense.