IMPORTANCE: Familial hypercholesterolemia (FH) is characterized by elevated cholesterol concentrations early in life. Untreated FH is associated with premature cardiovascular disease in adulthood. OBJECTIVE: To systematically review the evidence on benefits and harms of screening adolescents and children for heterozygous FH for the US Preventive Services Task Force (USPSTF). DATA SOURCES: MEDLINE, the Cochrane Central Register of Controlled Trials, and PubMed were searched for studies published between January 1, 2005, and June 2, 2015; studies included in a previous USPSTF report were also searched. Surveillance was conducted through April 8, 2016. STUDY SELECTION: Fair- and good-quality studies in English with participants 0 to 20 years of age. DATA EXTRACTION AND SYNTHESIS: Two investigators independently reviewed abstracts and full-text articles and extracted data into evidence tables. Results were qualitatively summarized. MAIN OUTCOMES AND MEASURES: Myocardial infarction and ischemic stroke in adulthood; lipid concentrations and atherosclerosis in childhood; diagnostic yield of screening; any harm of screening or treatment. RESULTS: Based on 2 studies (n = 83,241), the diagnostic yield of universal screening for FH in childhood is 1.3 to 4.8 cases per 1000 screened. There was no eligible evidence on the benefits or harms of FH screening in childhood. Eight placebo trials of statin drugs (n = 1071, 6-104 weeks) found low-density lipoprotein cholesterol (LDL-C) decreases of 20% to 40%; 1 trial (n = 214) showed a 2.01% decrease in carotid intima-media thickness with statins, compared with 1.02% with placebo (P = .02). Three placebo trials of bile acid-sequestering agents (n = 332, 8-52 weeks) showed LDL-C reductions of 10% to 20%. In 1 trial (n = 248), ezetimibe with simvastatin resulted in greater LDL-C reductions compared with simvastatin alone at 33 weeks (mean, -54.0% [SD, 1.4%] vs -38.1% [SD, 1.4%]). One trial of ezetimibe monotherapy (n = 138) showed mean LDL-C decreases of 28% (95% CI, -31% to -25%) from baseline and negligible change with placebo at 12 weeks. Eighteen studies found statins generally well tolerated. One observational study found lower, but still normal, dehydroepiandrosterone sulfate concentrations in statin-treated males with FH at 10-year follow-up. Bile acid-sequestering agents were commonly associated with adverse gastrointestinal symptoms and poor palatability. There was no eligible evidence on the effect of FH treatment on myocardial infarction or stroke in adulthood. CONCLUSIONS AND RELEVANCE: Screening can detect FH in children, and lipid-lowering treatment in childhood can reduce lipid concentrations in the short term, with little evidence of harm. There is no evidence for the effect of screening for FH in childhood on lipid concentrations or cardiovascular outcomes in adulthood, or on the long-term benefits or harms of beginning lipid-lowering treatment in childhood.