Only 29 cases of generalized melanosis caused by melanoma have been de
scribed in the English-language literature since the beginning of this
century. This is the first reported case in which the primary site of
melanoma was the mucosal surface of the rectum and melanosis was a pr
esenting sign of the disease. Generalized melanosis carries a dismal p
rognosis; none of the reported patients lived beyond 1 year after the
onset of pigmentation.