The authors report a 69‐year‐old woman with a hypercoagulable state manifesting as superior sagittal sinus thrombosis, thrombocytosis, right lower extremity deep venous thrombosis, and subsequent pulmonary embolus. The liver enzyme values were elevated in a cholestatic pattern. Carcinoembryonic antigen level was markedly elevated. Evaluation revealed that her longstanding “goiter” had slowly enlarged during the past 6 years. The serum calcitonin level was markedly elevated. Subsequent biopsy revealed medullary thyroid carcinoma. Surgical debulking of the tumor and lymph nodes resulted in substantial reduction of the calcitonin and carcinoembryonic antigen levels in a matter of days. Long‐term follow‐up revealed normalization of cholestasis and resolution of the hypercoagulable state. Review of the literature revealed no previously reported cholestasis or hypercoagulable state associated with medullary thyroid carcinoma. The literature on paraneoplastic cholestasis, carcinoembryonic antigen production, and hypercoagulable states is reviewed.