&NA;Two patients with myelofibrosis, a primary malignancy of the hematopoietic system, have developed carcinoid tumors of the rectum. This development is rare, as rectal carcinoids are more often associated with other carcinomas of the gastrointestinal tract. Rectal carcinoid tumors are, in general, less commonly associated with second malignancies than are carcinoid tumors of foregut and midgut origin