OBJECTIVES: To compare the effects of a low-carbohydrate (LC) diet with those of a low-fat (LF) diet on weight loss and serum lipids in overweight adolescents. DESIGN: A randomized, controlled 12-week trial. SETTING: Atherosclerosis prevention referral center. METHODS: Random, nonblinded assignment of participants referred for weight management. The study group (LC) (n = 16) was instructed to consume <20 g of carbohydrate per day for 2 weeks, then <40 g/day for 10 weeks, and to eat LC foods according to hunger. The control group (LF) (n = 14) was instructed to consume <30% of energy from fat. Diet composition and weight were monitored and recorded every 2 weeks. Serum lipid profiles were obtained at the start of the study and after 12 weeks. RESULTS: The LC group lost more weight (mean, 9.9 +/- 9.3 kg vs 4.1 +/- 4.9 kg, P <.05) and had improvement in non-HDL cholesterol levels (P <.05). There was improvement in LDL cholesterol levels (P <.05) in the LF group but not in the LC group. There were no adverse effects on the lipid profiles of participants in either group. CONCLUSIONS: The LC diet appears to be an effective method for short-term weight loss in overweight adolescents and does not harm the lipid profile.