Abnormal surgical bleeding may be caused by congenital or acquired plasmatic and/or thrombocytic coagulation disorders. They may be known at the time of operation, or they may occur during the perioperative course for the first time. A detailed identification of haemostatic defects can be performed by a diagnostic spectrum of multiple tests. However, in clinical practice global screening tests are used first. In diagnostic routine three groups of patients have to be considered: (1) patients with no personal or family history of bleeding and no operative bleeding risk; (2) patients with no history, but increased bleeding risk by the planned procedure; (3) patients with a known haemorrhagic diathesis in their own history. In all difficult situations a specialist in haemostasiology should be consulted, because only rational diagnosis and therapeutic monitoring achieve an optimal and cost-effective operative result. The surgeon should always be aware that surgical bleeding from an operative cause must be considered in the differential diagnosis.