Adenocarcinoma of the sigmoid colon in a 49year-old woman was resected without recurrence. Within a year she developed leukopenia and persistent generalized erythema. At 53, she acquired Coombs' positive hemolytic anemia and thrombocytopenic purpura which subsided after splenectomy. Erythema persisted and biopsies of her skin began to show the presence of mucin. She gained 13.6 kg (30 lb) in weight, and remained weak and became tired and depressed. At 56, the erythema gradually subsided. Her skin became puffy, thickened, swollen, and nonpitting. She developed hypercholesterolemia, low serum protein-bound iodine, and low radioactive iodine uptake which was not raised by thyroid stimulating hormone. Her serum was shown to contain circulating antibodies to human thyroglobulin. On thyroid medication administered orally, the patient is now well for the first time in eight years.