This cross-sectional study sought to identify the prevalence of medication adherence and to explore the role of depression and self-efficacy on medication adherence among patients with coronary artery diseases. Participants were recruited among outpatients who successfully underwent primary percutaneous coronary intervention (PCI) with drug-eluting stent at academic medical centres in Cheonan, South Korea. Medication adherence was evaluated by the eight-item Morisky Medication Adherence Scale using a validated Korean version. Prevalence of non-adherent to medication was 60.3%. With non-depressed and high self-efficacy as reference and after adjusting for age and gender, the models showed that those with depression and low self-efficacy are more likely to be non-adherent to medication. Therefore, future studies should focus on the development of interventions designed to reduce depression and increase self-efficacy for improving patient adherence to cardiovascular medications following PCI.