*Purpose: The functional nephron mass of an allograft is often taken into consideration when contemplating transplanting a small kidney into a large recipient. We aim to evaluate the impact of recipient-to-donor size mismatch on short term renal transplantation outcomes.

*Methods: We conducted a single-center cohort study of all patients who received a deceased donor kidney transplant between January 1^st, 1999, and December 1^st, 2020. Recipient race/ethnicity was identified via electronic health record. Size mismatch was assessed using weight as a surrogate marker for kidney size, classifying the cohort into the following (recipient weight/donor weight); smaller donor kidney (>1.25), weight-matched donor kidney (0.75-1.25), and larger donor kidney (<0.75). Outcomes measures included one-year graft and patient survival, and presence of delayed graft function (DGF). DGF was defined as a dialysis requirement within the first postoperative week. Differences across the weight mismatch groups were assessed using Pearson Chi-Square tests.

*Results: During the study period, 1378 deceased donor kidney transplants were performed. 76 recipients who had graft loss secondary to surgical or immunological complications in the first 3 months post-transplantation were excluded from the study. The remaining cohort of 1302 transplants was stratified as follows: smaller kidney (n=441, 33.8%) weight-matched kidney (n=676, 51.9%), and larger kidney (n=185, 14.2%). The groups had similar Kidney Donor Profile Index (KDPI) scores (42%, 42%, 41%) and cold ischemic times (17, 17.4, 16.3 hours). Patients recorded as “Black” were the most prevalent race/ethnicity in all three groups (65.3%, 68.2%, 62.2%). The DGF rates in the three groups were comparable (36.05%, 36.54%, 35.67%). The one-year patient survival in the three groups was 95.92%, 94.23%, and 96.76%. The one-year graft survival in the larger kidney group was superior to the weight-matched and smaller kidney group (95.68% vs 92.75% and 92.97%) (p = 0.420).

*Conclusions: Our data demonstrate comparable DGF rates as well as one-year graft and patient survival for both weight-matched and smaller donor kidneys. In comparison, the large donor kidney group had better one-year graft and patient survival rates.

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