Endocrine tumors may produce secondary or “ectopic” hormones that cause paraneo-plastic syndromes. Such syndromes may be confused with more common complications related to a patient's tumor, and thus escape detection and appropriate treatment. The secondary hormone secretion responsible for these syndromes often occurs late in the course of such diseases and presents in an insidious manner. Two patients are presented that illustrate these points. The first, a woman with medullary carcinoma of the thyroid (MCT), developed a syndrome secondary to ACTH secretion that was confused initially with the changes caused by the massive diarrhea that accompanies MCT. The second, a man with malignant glucagonoma, is the first with this disease to have developed symptomatic hyperin-sullnemia as a late complication. We stress the clinical courses of these patients and note that treatment of these syndromes may improve the quality of patients' lives.