Background and Objectives: Blood transfusion has been shown to be a risk factor for non-Hodgkin's lymphoma (NHL). Materials and Methods: In a cohort of 77,928 women with bleeding complications at delivery in the period of 1973–1986, subsequent NHL cases were identified and the number was compared with the number expected from national incidence rates. In a case-control study the proportion of transfused NHL cases was compared with the proportion of transfused controls. Results: The observed number of NHL in the cohort was 18 versus 22.0 expected. Information on transfusion was obtained for 15 of the NHL cases and none (0%) was transfused versus 32 out of 136 controls (23%). Conclusions: Blood transfusion at delivery is not a risk factor for NHL. The immune tolerance induced by pregnancy may reduce the risk of NHL associated with the transfusion of allogeneic blood cells.