Over the past few decades, the prevalence of overweight and obesity has significantly increased among adolescents of developed countries and becoming an emerging problem in countries undergoing socioeconomic transition. The adverse health outcomes resulting from overweight and obesity include short-term psychosocial problems and long-term non-psychological problems such as high blood pressure and type-2 diabetes. The objective of this study was to assess the prevalence and associated factors of overweight and obesity among high school adolescent in urban communities of Hawassa city. A cross-sectional study was conducted from February 20 to March 9/ 2012 among 559 secondary school students aged 10 to 19 years old in Hawassa city. A self-administered questionnaire was used to collect demographic, socio-economic, dietary and physical activity data. All anthropometric measurements of weight, height and TSFT were performed by using calibrated equipments and standardized techniques. The data was analyzed using SPSS for windows version 16 and WHO Anthro-Plus programs. Statistical tests for significance were performed at 5% level of significance. The results showed that the prevalence of overweight in the study participants was 12.9% and the prevalence of obesity was 2.7% based on age and sex specific BMI classification while based on TSFT, the prevalence of overweight and obesity was 11.0% and 3.8% respectively. Statistically significant agreement was observed between the tools (k= 0.841; p <0.001). The present study also found that there were a statistically significant association between sex, total physical activity, socio economic index, consumption frequency of meat, fruit, fast food and time spent watching TV/using computer with overweight and obesity prevalence (p<0.05). The present study revealed that more than one tenth of adolescents were overweight, making it a hidden problem of Hawassa city. The causes of overweight and obesity among adolescents aged 10-19 years in the study area may be many and complex but it might stem basically from the life style of adolescents. This information is useful for the planning of health and nutrition programs as well as intervention strategies to combat adolescent overweight and obesity.