This study was a 1-year clinical study on 16 (7 males and 9 females) pediatric patients with heterozygous familial hypercholesterolemia treated with hypocholesterolemic diet only, or with diet plus drug (simvastatin 10 mg/day). According to the study protocol, the children were submitted to a 3-month washout (free diet). Then they were given a diet (American Heart Association, step 2) for 6 months. After 6 months they were divided into two groups matched for sex, age and body mass index (BMI). Diet only was given to group A (n = 8); simvastatin (10 mg/daily) was given to group B, for 1 year. All patients were examined at baseline, and monitored for safety during the study by pediatricians. All patients were submitted to noninvasive cardiovascular examinations (exercise electrocardiogram, echocardiography). After 12 months of treatment with simvastatin, total cholesterol (TC) and low density lipoprotein cholesterol (LDLC) showed a statistically significant reduction (group B). The decrease of TC and LDLC in patients on diet only was 4% and 3% (all) and 17% and 4% (group A) after 6 and 12 months, respectively.