BACKGROUND: Routine pretransfusion testing for red cell alloantibodies (RBCab) in cesarean patients is standard practice in many obstetric centers. The objective of the present study was to evaluate the usefulness of this test. METHOD: A retrospective study was conducted using computerized registers to extract data on blood transfusions and the occurrence of RBCab in cesarean patients. RESULTS: A total of 4434 admissions for cesarean section were identified. Only 10 patients (0.23%) had clinically significant RBCab, which had not been previously detected. Blood transfusions were required in relation to 147 cesarean sections (3.3%). A number of preoperative conditions, traditionally believed to be risk factors for preoperative and postpartum hemorrhage, occurred more frequently in transfused patients than in nontransfused. The probability of a cesarean patient having a previously undetected clinically significant RBCab and receiving a blood transfusion during admission for delivery was estimated to be 9.0 x 10(-5) (1 in 11 050 cesarean sections). Analyses of the time relationships between cesarean sections and initiation of blood transfusions indicated that most often there would be enough time for postoperative antibody screening and/or cross matching if the routine pretransfusion testing was omitted. CONCLUSION: These findings suggest that routine pretransfusion testing in cesarean patients can be omitted.