Administrative claims data facilitate ascertainment of outcomes not collected by the transplant registry and provide the opportunity to examine prescribed doses of immunosuppressive medications. Here, we examine the impact of human leukocyte antigen (HLA) matching on traditional outcomes, rejection and survival, and use novel methods to examine immunosuppresion doses and complication rates. The central hypothesis tested in this analysis is that HLA-matched recipients receive lower doses of immunosuppression and have fewer posttransplant complications. We break from tradition by examining HLA matching in both living and deceased donor kidney transplants. As secondary aims, we compare the relative impact of class I and II mismatches and describe outcomes achieved with older donors. Medicare claims linked to the United States Renal Data System database for 23,443 kidney transplants were included in the study. A total of 15,793 transplants were DR mismatched (DRMM), 5,340 manifested no DR mismatches (NODRMM), and 2,310 manifested no ABDR mismatches (NOABDRMM). Patients with NOABDRMM experienced lower adjusted risk of rejection (0.66, 95% confidence interval 0.59-0.74, P < 0.001) and lower hazard of graft loss (0.69, 0.61-0.77, P < 0.001) and death (0.76, 0.63-0.92, P < 0.001) compared with those with DRMM. The hazard of cardiac and diabetic complications was similar between recipients of NOADRMM and DRMM transplants, but the hazard of diarrhea was significantly lower (0.82, 0.73-0.92, P < 0.001) in patients with NOABDRMM. The 6-month dose of mycophenolate mofetil was lower in patients with NOABDRMM. This study validates previous studies that indicated significantly lower risks of rejection, graft loss, and death among patients with 0 HLA-A,B,DR mismatches. Use of administrative claims revealed similar rates of cardiovascular complications. However, HLA-matched deceased donor recipients received lower dosages of mycophenolate mofetil and manifested a lower risk of developing posttransplant diarrhea.