bstract Objective: This study was done to investigate the effect of preoperative peer education on patients' adherence to medication and lifestyle changes after Coronary Artery Bypass Graft (CABG). Methods: In this randomized clinical trial, the peers of CABG patients conducted preoperative educational sessions at the ward in groups of 4-5 (n = 36) while the control group (n = 34) received routine education by a nurse. Adherence of both groups to medication and recommendations for lifestyle modification including physical activity, smoking, and diet was measured one and two months after discharge. Results: A multivariate analysis of co-variance showed the significant effect of peer education on adherence (F = 32.586, p < 0.001; eta(2) = 0.671). Univariate ANCOVA revealed a significant difference in adherence to diet between the two groups (F = 62.316, p = 0 0.0001; eta(2) = 0.482). Based on the repeated measures ANOVA, peer education significantly improved the CABG patients' adherence to diet (F = 55.373, p = 0.0001) and their total adherence (F = 9.911, p = 0.002) compared to the control group. Conclusion: Preoperative peer education had a significant effect on improving CABG patients' adherence to lifestyle changes after hospital discharge. Practice implication: Peer education can be used as an effective method to improve the CABG patients' adherence to lifestyle changes. (c) 2019 Elsevier B.V. All rights reserved.