Hematin has been shown to be effective therapy for acute intermittent porphyria. Few complications have been found. We cared for a patient who developed a markedly prolonged prothrombin time, partial thromboplastin time, thrombocytopenia, mild hypofibrinogenemia, mild elevation of fibrin split products, and a 10% fall in hematocrit while receiving hematin. No other cause for the coagulopathy could be found. The abnormal coagulation variables returned to normal when hematin was discontinued. Patients receiving hematin for acute intermittent porphyria should be closely observed for signs of coagulopathy.