This report concerns nine patients with carcinoma arising in mucous membranes included in a field of radiation therapy; the therapy had been administered previously for benign or malignant disease of other tissues or organs. The tumors recorded here comprise six squamous-cell carcinomas—two of the hypopharynx, two of the tongue, one of the buccal mucosa, and one of the anal canal—and three adenocarcinomas—two of the colon and one of the esophagus. Six of these tumors can, with reasonable certainty, be considered a late result of irradiation; with the three others the origin in irradiated areas makes it highly probable that radiation was a basic factor in the tumor development. Case 1. —A 53-year-old woman was first seen in May of 1948. She gave a history of having had a malignant tumor of the left parotid gland surgically removed in 1939. This was followed by a series of external x-irradiation treatments which