Summary: Background: Diabetes mellitus (DM) is a risk factor for peripheral arterial disease (PAD). Indications for open surgery in infrainguinal intermittent claudication (IC) are limited, and reports are lacking regarding outcomes in DM patients. Study aims were to compare short and long-term effects on major adverse cardiovascular events (MACE), acute myocardial infarction (AMI), stroke, major amputation, and mortality after infrainguinal open surgery for IC in patients with and without DM, and to evaluate relationships between glycaemic control and outcomes. Methods: Nationwide observational cohort study of all patients registered in the Swedish Vascular Registry after planned infrainguinal open surgery for IC from January 1st 2010 to December 31st 2014. Patients registered in the National Diabetes Registry were compared with patients without diabetes by propensity score adjusted comparison of MACE, AMI, stroke, major amputation, and mortality. Results: After 30 days, there were no differences in MACE, AMI, stroke, major amputation, or mortality between patients with (n = 323, mean age 70.5 [SD 7.4] years, 92 [28.5%] females) and without (n = 679, mean age 69.7 years [SD 11.2], 234 [34.5%] females) DM. At last follow-up after median 5.2 years, patients with DM showed higher rates of MACE (Hazard ratio [HR] 1.33, confidence interval [CI] 1.08-1.62; p < 0.01), and AMI (HR 2.21, CI 1.46-3.35; p < 0.01) than patients without diabetes. Among DM patients, higher glycated haemoglobin (HbA1c) was associated with higher rates of MACE (HR 1.02, CI 1.00-1.03; p = 0.02), stroke (HR 1.05, CI 1.00-1.11; p = 0.04), and total mortality (HR 1.03, CI 1.01-1.06; p < 0.01), during follow-up, whereas duration of diabetes was associated with higher rate of major amputation (HR 1.08, CI 1.02-1.15; p < 0.01). Conclusions: DM patients showed higher rates of MACE and AMI in propensity score adjusted analysis five years after planned infrainguinal open surgery for IC. Higher HbA1c was associated with MACE, stroke, and total mortality in patients with DM, whereas longer duration of DM was associated with major amputation.