Purpose: We aimed to study the utilization patterns of lipid-lowering treatment (LLT), including treatment modification, adherence, and possible statin intolerance , in patients with atherosclerotic cardiovascular disease (ASCVD) or diabetes using national claims data in South Korea. Methods: A retrospective cohort study was conducted using data from the Korean Health Insurance Review & Assessment Service claims database. Patients aged >= 18 years with > 1 outpatient pharmacy claim for a statin and/or ezetimibe dated January 1, 2012, to December 31, 2014, were identified and categorized into the following cohorts: patients with ASCVD, and patients with diabetes mellitus without ASCVD. LLT modification, adherence to index LLT, and possible statin intolerance were explored during the 12 months after the date of first prescription for a statin and/or ezetimibe. Findings: Among 1,399,872 patients who met the eligibility criteria, 807,547 (57.7%) were patients with ASCVD and 592,325 (42.3%) were patients with diabetes without ASCVD. About half of the patients had no modification in their index treatment (46.2% in the ASCVD cohort and 48.9% in the diabetes cohort), and the most common modification was permanent discontinuation (19.6% in the ASCVD cohort and 21.4% in the diabetes cohort). The mean medication possession ratios were 0.77 in the ASCVD cohort and 0.73 in the diabetes cohort and showed a decreasing trend during the 12-month follow-up period. Among patients who initiated a statin and/or ezetimibe, possible statin intolerance was observed in 53,921 patients (6.7%) in the ASCVD cohort and 42,172 patients (7.1%) in the diabetes cohort. (C) 2018 Elsevier HS Journals, Inc. All rights reserved.