BACKGROUND: Evolocumab is the first monoclonal antibody against proprotein convertase subtilisin/kexin type 9 approved in Japan for familial hypercholesterolemia (FH) and hypercholesterolemia; however, data on its safety and effectiveness in the real-world setting in Japan are limited. METHODS AND RESULTS: This real-world, postmarketing, single-arm study assessed the safety and effectiveness of low-density lipoprotein cholesterol lowering with evolocumab in patients with homozygous/heterozygous familial hypercholesterolemia and hypercholesterolemia with high risk in Japan (668 sites). The primary safety end point was the incidence (percentage) and number of patients with adverse drug reactions and serious adverse events during the 104-week follow-up. Primary effectiveness end points included the percentage change in low-density lipoprotein cholesterol levels from baseline to week 12, assessed using 2-sided paired tests. The safety and effectiveness sets comprised 3724 (homozygous FH, n=108; heterozygous FH, n=2009; hypercholesterolemia with high risk, n=1607) and 2797 (homozygous FH, n=91; heterozygous FH, n=1615; hypercholesterolemia with high risk, n=1091) patients, respectively. Overall, mean age and disease duration were 63.2 and 12.3 years, respectively. Serious adverse drug reactions and serious adverse events were experienced by 0.5% and 10.3% of patients; the incidence rates of myocardial infarction and stroke were 0.7% and 0.3%, respectively. A significant mean±SD percentage change in low-density lipoprotein cholesterol levels was observed at week 12 among patients with homozygous FH (-45.7%±28.2; <0.001), heterozygous FH (-55.9%±28.8; <0.001), and hypercholesterolemia with high risk (-63.3%±23.7; <0.001). CONCLUSIONS: Evolocumab was well tolerated, and real-world patients with familial hypercholesterolemia and hypercholesterolemia with high risk in Japan had sustained low-density lipoprotein cholesterol reduction. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique Identifier: NCT02808403.