BACKGROUND: Diabetes is a risk factor for postoperative morbidity, which includes total hip and knee arthroplasty. However, no previous studies have been done in a fast-track setting with optimized perioperative care, including spinal anesthesia, multimodal opioid-sparing analgesia, early mobilization, and discharge to home, which improved postoperative outcome. METHODS: We performed an observational cohort study using prospective data in primary total hip and total knee arthroplasty with a standardized fast-track approach. Eight hundred ninety type 2 diabetics were successfully propensity matched with 7165 nondiabetics. Subanalyses on antihyperglycemic treatment were done using the Danish National Database of Reimbursed Prescriptions for information on dispensed prescriptions 6 months preoperatively. Length of hospital stay (LOS), 90-day readmissions, and mortality were found through the Danish National Health Registry and medical charts. Multiple logistic regression analyses on LOS > 4 days and readmissions were used to further adjust for demographics, comorbidity, and department of surgery. To further evaluate the clinical relevance of type 2 diabetes, we estimated the number of surgical type 2 diabetics needed for 1 more occurrence of LOS > 4 days or readmissions (adjusted number needed to harm [NNH]). RESULTS: Although more type 2 diabetics (11.3%) than nondiabetics (8.1%) had LOS > 4 days (unadjusted P = 0.001), there was no association between type 2 diabetes and LOS > 4 days when adjusting for covariates (odds ratio: 1.19 [0.93–1.54]; P = 0.172). Correspondingly, the NNH was 78 but ranged between 31 and infinity. Type 2 diabetes was not associated with 30- (1.02 [0.75–1.39]; P = 0.897) or 90-day readmissions (1.22 [0.87–1.71]; P = 0.254), and with an NNH of 957 (59–[infinity]) and 115 (35–[infinity]), respectively. Insulin-treated type 2 diabetes was associated with increased risk of specific “diabetes-related” morbidity (1.95 [1.13–3.35]; P = 0.016). CONCLUSIONS: Type 2 diabetes per se has limited influence on postoperative morbidity in fast-track total hip and knee arthroplasty.