Shortages of O-negative red blood cells are becoming increasingly common, forcing hospitals' blood transfusion services to find solutions to conserve this blood group for patients who need it most. The present study aimed to retrospectively evaluate the practice of transfusing selected RhD-negative patients with RhD-positive red blood cells and to assess the impact of this measure on patients and blood transfusion service management. Transfusion data of 1199 RhD-negative patients hospitalised at Cliniques Universitaires Saint-Luc between 2019 and 2022 were analysed. For patients who received RhD-positive red blood cells, age, gender, reason for hospital admission, indication for transfusion, and immunohematology analyses were recorded. These data enabled an assessment of transfusion practices over the years, characterisation of patients who received RhD-mismatched transfusions, determination of the alloimmunisation rate, and calculation of the total number of RhD-negative red blood cells saved. During the study period, 141 RhD-negative patients received 604 RhD-positive red blood cells. A change in transfusion practices was observed over the years, with a greater proportion of RhD-negative patients being transfused with RhD-positive red blood cells in 2022 (28%) compared to 2019 (2%). The overall alloimmunisation rate was at least 20%, and 416 red blood cells were saved without any consequences. Patients undergoing cardiovascular surgery received the highest number of RhD-positive red blood cells. The transfusion of selected RhD-negative patients with RhD-positive red blood cells is a low-risk practice that helps conserve RhD-negative red blood cells. However, there is a minimum 20% risk of alloimmunisation, which could have clinical and transfusion-related consequences in the future.