Depression of the vitamin K-dependent modulators of coagulation during the initial phase of oral anticoagulant therapy may lead to a transient hypercoagulable state and skin necrosis. We report a case of skin necrosis associated with inherited protein S deficiency following prolonged coumarin therapy. As a result of a stasis ulceration causing a rise in c4b binding protein and concurrent treatment with topical sulfonamide, we hypothesize that a precipitous decrease in free protein S led to skin necrosis. Progression of the necrosis was halted with unactivated prothrombin complex concentrate. This case confirms the rare association between coumarin induced skin necrosis and protein S deficiency and emphasizes potential drug interactions.