Heterozygous familial hypercholesterolemia (HeFH) is a genetic disorder characterized by elevated levels of low-density lipoprotein cholesterol (LDL-C). This phase 2 dose-finding study (NCT02890992) evaluated the efficacy, safety, and dose selection of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor alirocumab in pediatric HeFH patients. HeFH patients (n = 42) who were aged 8–17 years, had body weight (BW) ≥25 kg, and had LDL-C ≥130 mg/dL despite optimal statin/other lipid-modifying therapies were enrolled in 4 cohorts according to BW: cohort #1: 30 mg (<50 kg) or 50 mg (≥50 kg) every 2 weeks (Q2W), #2: 40 mg (<50 kg) or 75 mg (≥50 kg) Q2W, #3: 75 mg (<50 kg) or 150 mg (≥50 kg) every 4 weeks (Q4W), #4: 150 mg (<50 kg) or 300 mg (≥50 kg) Q4W. Primary endpoint was LDL-C % change from baseline to week 8. Mean age was 12.4 years and 95% of patients were on a statin. Baseline LDL-C levels were 160.0–188.9 mg/dL and free PCSK9 was 186.4–201.7 ng/mL across the cohorts. At week 8, the higher dose cohorts (2 and 4) demonstrated the greatest reductions in LDL-C (–46% and –45%, respectively). Free PCSK9 levels were lowest at week 8 in cohorts 2 and 4 (42.2 ng/mL and 8.6 ng/mL, respectively). Adverse events were reported in 50–90% of patients across the cohorts, and 2 patients discontinued due to adverse events. In pediatric HeFH patients, LDL-C reductions were greatest in the higher dose cohorts. Alirocumab was generally well tolerated at all doses. Display omitted •Heterozygous familial hypercholesterolemia is underdiagnosed in children, placing them at risk of cardiovascular events.•Target low-density lipoprotein cholesterol levels are often not reached despite optimal lipid-modifying therapies.•We assessed the effects, safety, and doses of alirocumab in pediatric patients with heterozygous familial hypercholesterolemia.•Reductions in low-density lipoprotein cholesterol were observed across all assessed doses.•Overall, treatment with alirocumab was generally well tolerated.