INTRODUCTION: Implanon is a widely used contraceptive. It is a progestagen-containing implant which is inserted subcutaneously on the inside of the upper arm. This procedure is relatively simple. CASE DESCRIPTION: A 26-year-old woman had her contraceptive implant replaced in the outpatient clinic. Because of a mechanical heart valve, she used phenprocoumon, which she did not discontinue prior to the procedure. Three days after the Implanon replacement, the patient presented with persistent blood loss from the insertion site and a large hematoma around the new implant. The placement of a new pressure bandage was not sufficient. The concentration of Hb fell from 8.1 to 5.0 mmol/l with an INR of 3.5; therefore, the patient received a blood transfusion. The use of phenprocoumon was temporarily discontinued and the INR was corrected with prothrombin complex. Good hemostasis was ultimately achieved. CONCLUSION: Although the replacement of a subcutaneous hormone implant is a relatively simple procedure, a severe complication such as hemorrhaging may occur, particularly when there are risk factors.