Hypofibrinogenemia and Factor XI deficiency are rare defects of hemostasis, potentially leading to spontaneous bleeding manifestations and increased bleeding risk during surgery, dentistry, and interventions. Due to the different mode of inheritance, the concomitance of both defects is extremely rare and the clinical management of combined hypofibrinogenemia and factor XI deficiency is not standardized. Here, we report a rare case of concomitant genetically determined hypofibrinogenemia and factor XI deficiency as a cause of increased spontaneous bleeding and bleeding complications during dentistry. The diagnostic procedure including screening assays, single clotting factor determinations, genetic analyses, and also use of thrombin generation assays (TGA) are described. Also, we present our considerations regarding the development of an adequate prophylaxis of bleeding with fibrinogen concentrate in this case. The literature regarding the issue is briefly discussed.