Purpose: This study was conducted to measure medication adherence and perceptions of anticoagulation therapy and its relationship to patients taking warfarin. Methods: In a cross-sectional survey, 150 patients taking warfarin who had visited an outpatient clinic of a cardiovascular center in Seoul were included as research subjects. Medication adherence was measured using a visual analogue rating scale (VAS). Barriers and attitudes toward adherence, and oral anticoagulation knowledge, were measured using a structured questionnaire. Participants’ medical records also were reviewed to identify clinical characteristics. Results: About one third of the participants (30.7%) reported medication adherence as 100%. The major barriers to adherence were identified as “Forgetting the time of medication” and “Not carrying their medication’’. Overall attitudes toward medication adherence were high, but oral anticoagulation therapy knowledge was low. To determine the relationship of medication adherence and perceptions of anticoagulation therapy, participants were stratified into three groups, based on their medication adherence levels (high adherence, moderate adherence, low adherence). Participants in the high adherent group more likely to be older (OR: 1.04, 95% CI: 1.005-1.071) and to have positive attitudes toward medication adherence (OR: 1.12, 95% CI:1.013-1.229) compared to the other two groups. Conclusion: The results show that age and attitude exerts significant influence on medication adherence in patients taking warfarin.