Background <p>This study assessed de novo human leukocyte antigen (HLA) antibodies associated with blood transfusions in a paediatric kidney transplantation cohort, associated risk factors and outcomes.</p> Methods <p>Patients with kidney disease at Royal Children’s Hospital (Melbourne, Australia) who were transfused and/or received a kidney transplant between 2000 and 2018 were included. HLA antibody results from pre- and post-transfusion serum specimens, blood donor typing (where available) and clinical and laboratory data were collected. A control group comprised non-transfused patients from the same cohort. The primary outcome was the incidence proportion of de novo blood donor specific HLA antibodies (bDSA). Secondary outcomes included risk factors, including eplet mismatches with the blood donor, kidney donor and both.</p> Results <p>Screening identified 123 transfused and 63 non-transfused patients, with 34 and 28, respectively, included. Transfused patients were younger. At mean fluorescence intensity (MFI) cutoff 500, 36.7% of transfused patients developed de novo HLA class 1 bDSA and 23.3% de novo HLA class 2 bDSA. Overall, de novo HLA class 1 and class 2 antibodies were non-significantly higher in the transfused group (64.7%/55.9%) than in the non-transfused group (46.4% for both, <i>p</i> = 0.200 and <i>p</i> = 0.610, respectively). Risk factors identified included younger age (<i>p</i> &lt; 0.05) and rhesus factor D (RhD) negative status (<i>p</i> = 0.021). The number of shared eplet mismatches was associated with corresponding de novo HLA antibodies (<i>p</i> = 0.02).</p> Conclusions <p>Blood transfusion can be associated with bDSA in paediatric kidney disease, especially with shared blood and kidney donor mismatches. Strategies to avoid sensitisation, such as HLA selection of blood donors, may reduce this risk.</p> Graphical abstract <p></p>