The purpose of this study was to determine whether patients with diabetes mellitus (DM) have a higher likelihood of immediate, inpatient complications following primary and revision total hip (THA) and total knee arthroplasty (TKA) than patients without DM. From 1988 to 2003, the Nationwide Inpatient Sample identified 751340 primary or revision THA or TKA patients. 64262 (8.55%) had DM. Comparisons of specific outcome measures between diabetic and nondiabetic cohorts were performed using bivariate and multivariate analyses with logistic regression modeling. Diabetic patients had fewer routine discharges and higher inflation-adjusted hospital charges for all procedures. Although complications were not uniformly increased, diabetic patients had significantly increased odds of pneumonia, stroke, and transfusion (P < .001) after primary arthroplasty. This analysis of a large patient database indicates clinically relevant information for patients and surgeons, suggesting that patients undergoing THA and TKA demonstrate more complications and utilize more resources if they have the comorbidity of DM level II evidence.