This study was done to investigate effects of smoking, drinking and exercise on body composition, dietary intakes, serum lipids of male high school students in Seoul. Body Composition was analyzed by the Bioelectrical Impedance Fatness Analyzer. Dietary survey was conducted by 24-hour recall method and nutrient intakes were analyzed by the Computer Aided Nutritional analysis program for professional (CAN-Pro). All data were statistically analyzed by SAS PC package program. Mean and standard error were examined for each items. The significant difference was examined by student`s t-test. Body composition data showed that protein mass, mineral mass and lean body mass of regular exercisers were significantly higher (p < 0.05) than those of irregular exercisers. Energy and protein intakes of male high school students were 1868 kcal/day (69.2% RDA), 68 g/day (91.3% RDA), respectively. Ca, Fe and Vitamin B2 intakes were lower than 2000 RDA. Analysis of serum lipids showed that serum levels of HDL-cholesterol of drinkers were significantly higher (p < 0.05) than those of nondrinkers. Overall results imply that smoking and alcohol drinking of adolescent males may not much influence on serum lipids levels because pack-years of smoking or the amount of alcohol drinking was not serious enough to be harmful to health. (Korean J Community Nutrition 9(1): 19~28, 2004)