Of 120 patients presenting with mild bleeding disorders, 63 were found to have a definite coagulopathy. The commonest disorders were haemophilia, Christmas disease and von Willebrand's disease (vWd), the latter being predominant. Diagnosis led to prophylactic treatment prior to surgery in 18 patients with prevention of excessive haemorrhage. Three patients who had received blood products developed hepatitis. DDAVP (desamino-cys-1-8-D-arginine vasopressin) is the treatment of choice in suitable mildly affected patients with haemophilia A and vWd. Examination of blood group distribution suggests an excess of group O among patients with bleeding disorders, especially those with vWd.