Summary. Surgery performed without blood component therapy in patients with severe factor XI deficiency can be accompanied by excessive bleeding in some but not all patients. In an attempt to minimize the use of blood derivatives, we carried out a retrospective analysis of bleeding complications in 120 patients with severe FXI deficiency (level of <1–15 U dL−1) who had undergone different types of surgical procedures without replacement therapy. Procedures at tissues exhibiting fibrinolytic activity were associated with bleeding in 49–67% of the patients, while procedures involving sites with no local fibrinolytic activity were associated with bleeding in 1.5–40%. The increased bleeding tendency at fibrinolytic site was significant (P = 0.0015), but was unrelated to the genotype of the patients. Thus, parsimonious use of replacement therapy is possible in patients with severe FXI deficiency undergoing surgery predicting a decrease in the risks of volume overload, transfusion related acute lung injury, transmission of infectious diseases, thrombosis, allergic reactions and development of inhibitors to FXI.