Background: Malnutrition is the most serious human health and social problems that affect vast population of the world. Malnutrition continues to be a major public health problem throughout the developing world, particularly in southern Asia and sub-Saharan Africa. Adolescents from developing countries are more vulnerable to nutritional deficiencies due to early childhood nutritional problems, which include underweight, stunting and low dietary intakes Objective: To assess determinants of under nutrition among adolescents in Burayu woreda, Oromia Region, May 2011. Methods and materials: Community based unmatched case-control study design was conducted in Burayu woreda, Oromia Region from 10-25 March 2011. Cases comprised undernourished adolescents aged 10-19 years and controls were well-nourished adolescents. The study subjects were selected with probability proportional to size from the six kebeles. Using simple random sampling technique data was collected from 91 cases and 91...