OBJECTIVE Neoplastic lesions containing both an adenomatous component and a carcinoid component are rare. To our knowledge, only two such lesions have been reported previously in the large intestine. We report two additional cases to further delineate the histologic features of these lesions and discuss their possible origin. METHODS Cases from the surgical pathology files, including consultation material, of the University of Cincinnati (Ohio) were reviewed. METHODS One patient refused repeat colonoscopy at 6 months and subsequently was lost to follow-up. The other patient died 26 months after a hemicolectomy without evidence of recurrence. RESULTS One lesion represents a collision tumor in which the two histologic components lay adjacent to one another without intermingling. The other is a composite tumor in which the components intermingled in such a way that in some areas the two components were difficult to distinguish from one another. CONCLUSIONS Although both lesions contain dual components, we believe they are fundamentally different and that they arose from different mechanisms. Definite conclusions regarding prognosis cannot be made owing to the rarity of these lesions; however, there is no evidence to suggest they behave aggressively.