Summary OBJECTIVE Hypothyroidism can be complicated by bleeding symptoms such as easy bruising, menorrhagla and sometimes even a severe bleeding tendency with fatal outcome. Usually there is a prolonged bleeding time, or a low plasma concentration of coagulation factor VIII (FVIII) or von Willebrand factor (vWF). The aim of the present study was to investigate the acute haemostatic effect of desmopressin in hypothyroid patients. Another aim was to study the long‐term effect of thyroxine replacement on the plasma concentrations of coagulation factors and to ascertain the duration of thyroxine treatment needed to restore haemostatic function. DESIGN AND PATIENTS The effects of desmopressin, given intravenously over 10 minutes at a dosage of 0.3 μg/kg, and thyroxine treatment on haemostatic function were studied prospectively In 10 patients with hypothyroidism. RESULTS Before treatment only five of the patients manifested bleeding symptoms; one had prolonged bleeding time, and one had low plasma concentrations of vWF: Ag. Desmopressin virtually immediately reduced bleeding time, enhanced platelet adhesiveness, and significantly increased plasma concentrations of FVIII and vWF. The plasma concentrations of FVIII and vWF showed a significant increase after 4 months, whereas 7 months treatment with thyroxine was needed to reduce bleeding time significantly. CONCLUSION Our results suggest that in hypothyroid patients desmopressin may be of value for the acute treatment of bleeding or as cover for surgery.