Objective. The present study was designed to evaluate the lipid-altering efficacy, safety, and tolerability of lovastatin treatment in adolescent girls with heterozygous familial hypercholesterolemia. Methods. A total of 54 postmenarchal girls, aged 10 to 17 years, were enrolled in a 24-week, double-blind, randomized, placebo-controlled study. After a 4-week diet/placebo run-in period, patients were randomized to 1 of 2 groups: ( 1) treatment with diet plus lovastatin 20 mg/day for 4 weeks, followed by diet plus lovastatin 40 mg/day for 20 weeks, or ( 2) diet plus placebo for 24 weeks. Results. Baseline values of lipids, lipoproteins, and apolipoproteins (apo) were comparable between treatment groups. Lovastatin treatment was efficacious at reducing low-density lipoprotein cholesterol by 23% to 27%, total cholesterol by 17% to 22%, and apo B by 20% to 23% at weeks 4 and 24, respectively. Between-treatment group differences were not statistically significant for triglycerides, very-low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or apo A-I. Lovastatin was generally safe and well tolerated. There were no clinically significant alterations in vital signs ( blood pressure and pulse rate), anthropomorphic measurements ( height, weight, and BMI),hormone levels ( luteinizing hormone, follicle-stimulating hormone, dehydroepiandrosterone sulfate, estradiol, and cortisol), menstrual cycle length, or tests of liver and muscle function. Conclusions. Lovastatin offers an efficacious and well-tolerated treatment option for improving lipid profiles in adolescent girls with familial hypercholesterolemia.