Abstract : Introduction: Obesity is an increasingly growing universal health issue. Due to the prevalence of obesity and its association with an increased risk of cardiovascular disease requiring surgical intervention, it is important that the medical students have a good knowledge of these two correlated conditions. Aim: To assess the students' perception on the relationship between body mass index (BMI) classes and the outcomes of coronary artery bypass grafting (CABG) surgery among medical student in King Faisal University in Alahsa, Saudi Arabia. Method: This is a cross-sectional study, participants underwent An 11-item questionnaire that included three sections. The first section included questions about demographic data in the form of gender and study year, the second section included questions about CABG surgery complications e.g. renal failure and respiratory failure, and the last section investigated the relationship between BMI classes and CABG complications. Conclusion: CABG is a major procedure that is associated with many complications, Therefore, it is important to raise the level of awareness for both present and future doctors about this relationship in order to improve the overall patient care and the outcomes for these patients.