OBJECTIVES: Examine: (1) the anthropometric, socio-demographic and use-of-time characteristics of thin adolescents, and (2) compare these characteristics to other weight status categories. METHODS: Data were from the 2007 National Children's Nutrition and Physical Activity Survey which collected data on a random sample of 2200 9 to 16 year old Australians from February to August 2007. Seven socio-demographic variables, anthropometric data (height and weight were measured) and nine use-of-time variables were used, and compared across the weight status categories. Physical activity was measured using pedometers and the Multimedia Activity Recall for Children and Adults. RESULTS: 5.3% of adolescents were classified as thin, a percentage which did not significantly vary by age, sex, indigenous status, household income, education level or family structure. Relative to other adolescents, thin adolescents were shorter and lighter. Thin adolescents were less active than their normal weight peers, but walked further and accumulated significantly less screen and TV time than obese adolescents. CONCLUSION: Thin adolescents were found in similar proportions across all socio-demographic bands. Thin adolescents recorded similar physical activity levels to their normal weight peers, but were more active than obese adolescents. The findings from the study support in part the theory of thinness related developmental delay.