The caecum and the ascending colon are the colon segments most frequently affected by tumoral synchronism. Synchronous colorectal carcinoma etiopathogenesis is complex and most likely by malignancy of preexisting adenomas (adenoma-adenocarcinoma sequence). The following tumoral synchronism clinical case's particularity is represented by the simultaneous diagnosis of a flat-type adenocarcinoma of the caecum (less common histopathological type) and of a mucinous adenocarcinoma on the ascending colon. Tumor profiles of both carcinomas were examined histologically and immunohistochemically, emphasizing: (1) tumor proliferation different histological type; (2) residual adenomas in the periphery of the flat-type adenocarcinoma; (3) hardly microscopic detectable invasive character of the flat-type carcinoma; (4) mucinous carcinoma's infiltrating character and its immunohistochemical phenotype; (5) both tumor aggressiveness.