OBJECTIVES:  Primary and revision total hip and total knee arthroplasties (THA and TKA, respectively) are increasing in frequency due in part to the aging population. The impact of preoperative comorbidities and patient presentation on post-operative complications is not well understood. METHODS:  Using MarketScan Commercial and Medicare databases (2009-2015), patients were identified by the following diagnosis (International Classification of Diseases, 9th edition (ICD-9)) or Current Procedural Terminology (CPT) codes within inpatient or outpatient settings: primary THA (P_THA: ICD-9 81.51 or CPT-4: 27130), primary TKA (P_TKA: ICD-9 81.54 or CPT-4: 27440-7), revision THA (R_THA: ICD-9 00.70-7, 81.53 or CPT 27134, 27137-38) and revision TKA (R_TKA: ICD-9 00.80-4, 81.55, CPT 27486-8). All patients had at least 365 days pre- and 90 days post-index continuous enrollment. Patients were categorized based on pre-existing diabetes (ICD 250.X), obesity (ICD 278.00, 278.01, 278.03, V85.35-45), osteoporosis (ICD 733.X) or smoking (ICD 305.X, V15.82) codes. Occurrence of 90-day infection (ICD 998.X, 686.9, 038.9, 711.05-6, 730.05-6) was queried for all patients. RESULTS:  The 90-day infection rates were 1.9% (4,828/260,801), 1.95% (2,511/130,617), 9.5% (1,361/14,331) and 6.7% (777/11,657) for P_TKR, P_THR, R_TKR and R_THR, respectively. For primary procedures, comorbidities with the greatest effect on the odds of infection were obesity (OR: 1.814, 95%CI: 1.640-2.007 for P_THR and 1.558, 95%CI: 1.454-1.669 for P_TKR) and diabetes (OR: 1.686, 95%CI: 1.541-1.846 for P_THR and 1.344, 95%CI: 1.262-1.430 for P_TKR). Osteoporosis had a small but statistically significant effect on the odds of infection for primary procedures. For revision procedures, only diabetes (OR: 1.468, 95%CI: 1.242-1.735 for R_THR and 1.309, 95%CI: 1.162-1.474 for R_TKR) and obesity (OR: 1.324, 95%CI: 1.061-1.653 for R_THR and 1.350, 95%CI: 1.176-1.550 for R_TKR) increased the odds of infection. CONCLUSIONS: Diabetes and obesity are significantly associated with 90-day infection rates in patients undergoing primary or revision total hip or knee replacements.