Synchronous carcinoma of the upper and lower gastrointestinal tract was encountered in 4 patients who presented with occult gastrointestinal blood loss. Observation of these 4 patients alerted us to the existence of such an entity and served to illustrate the fact that the finding of an index carcinoma may not be the only bleeding site in such patients. The preoperative detection of synchronous neoplasms not only allows an appropriate surgical strategy to be adopted, but facilitates the planning of a logical policy for follow-up. Awareness of this rarely documented association is important simply because the surgical implications in an individual case are significant.