Objectives: Coronary artery bypass grafting improves outcomes in patients with multi-vessel coronary artery disease. Bypass of angiographically significant lesions ≥70% is recommended, yet little is known about the incidence/outcomes with bypasses of 50-69% angiographically borderline lesions without fractional flow reserve testing. The objective of this study was to investigate the incidence and outcomes of bypass of 50-69% angiographically borderline lesions. Methods: Between 2007 and 2013, 3,195 patients underwent isolated first multi-vessel coronary artery bypass grafting at the Mazankowski Alberta Heart Institute. Patients with an isolated angiographically borderline lesion of a major epicardial vessel were included. The primary analysis compared clinical and angiographic outcomes between patients with and without coronary bypasses of angiographically borderline lesions. Outcomes of interest included time to all-cause mortality, 30 day, and 1 year mortality. Results: Among 350 patients with an angiographically borderline lesion, 268 (76.6%) had the vessel containing the angiographically borderline lesion bypassed while 82 (23.4%) did not. Mean follow-up was 4.2 years. Patients with a bypassed angiographically borderline lesion were older (66.1 vs 62.5 mean years, p=0.006) but otherwise similar in sex, comorbidities, diabetes, ejection fraction, and number of coronary stenoses. Cardiopulmonary bypass time was longer in patients with bypassed angiographically borderline lesions (104.2 versus 90.4 minutes, mean, p<0.001). Unadjusted overall mortality through end of follow-up was higher among patients with bypassed angiographically borderline lesions (11.6% versus 3.7%, p=0.034). After multi-variable adjustment, the association between angiographically borderline lesion bypass and mortality was attenuated (hazard ratio 2.84: 95% confidence interval, 0.87 – 9.23, p=0.080). No differences were observed in unadjusted 30-day (1.1% versus 0.0%, p=0.336) or 1-year mortality (4.1% versus 0.0%, p=0.062). Repeat revascularization of patients with bypassed angiographically borderline lesions was numerically higher (4.1% versus 0.0%, p = 0.107). Conclusions: In an unselected cohort of patients with angiographically borderline lesions, bypass of borderline 50-69% lesions is frequently performed and not associated with improved long-term survival. Our findings suggest that the routine surgical revascularization of 50-69% angiographically borderline lesions may not be warranted.