Understanding modifiable risk factors to improve surgical outcomes is increasingly important in value-based health care. There is an established association between peripheral artery disease (PAD), diabetes, and limb loss, but less is known about expected outcomes after revascularization relative to the degree of glycemic control. The purpose of this study was to determine the association between hemoglobin A1c (HbA1c) management in diabetics and surgical outcomes after open infrainguinal bypass. The Vascular Quality Initiative infrainguinal bypass module was used to identify adult patients (≥18 years) with a history of diabetes who underwent bypass for PAD between 2011 and 2018. Exclusion criteria included missing or illogical HbA1c values and if the indication for the limb treated was not PAD. Patients were categorized by preoperative HbA1c levels as low severity/controlled (<7.0%), high severity (7.0%-10.0%), and very high severity (>10.0%). Primary outcomes were 30-day incidence of major adverse cardiac events (MACEs), major adverse limb events (MALEs), ipsilateral amputation, and 1-year all-cause mortality. Thirty-day outcomes were calculated using multivariable regression to compute odds ratios; hazard ratios were calculated for all-cause mortality. All analyses were adjusted for demographics, comorbidities, and clinical characteristics. The final sample included 30,813 operations (27,988 unique patients): 17,517 (57%) nondiabetic patients, 5194 patients with low-severity/controlled diabetes, and 8102 (26%) patients with poorly controlled diabetes, including 5531 (70%) treated with insulin. There were 6439 (21%) patients with high-severity HbA1c values and 1663 (5%) patients with very-high-severity HbA1c values. Those with a very high HbA1c level were more likely to be nonwhite, insulin dependent, and active smokers. Compared with nondiabetics, patients with very-high-severity HbA1c had an 81% increase in MACEs and 31% increase in MALEs, whereas patients with high-severity HbA1c only had a 49% increase in MACEs and a 12% increase in MALEs. Each one-step increase in severity category (eg, low to high to very high) was associated with an average 29% increase in the odds of MACEs and an 8% increase in the odds of MALEs. Uncontrolled diabetes with an HbA1c value >10.0% was associated with significantly worse 30-day surgical outcomes. Patients with incrementally better glycemic control (HbA1c level of 7.0%-10.0%) did not suffer the same rate of complications, suggesting that preoperative attempts at improving diabetes management even slightly could lead to improved surgical outcomes in open infrainguinal bypass patients. Copyright © 2019 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.