Intestinal types of adenocarcinoma of the inner nose and colorectal adenocarcinoma present a stupendous similarity of morphological and immunohistochemical features. The previously unpublished observation of a synchronous manifestation of both adenocarcinoma enabled us to compare the tumors using molecular and immunohistochemical methods. Polymerase chain reaction was performed in order to investigate microsatellite instability. Mutation of p53 and K-ras was examined by direct DNA sequencing. Chromosomal imbalances were investigated by comparative genomic hybridization. Histology and immunohistochemical reactions were nearly identical. PCR results revealed no microsatellite instability or loss of heterozygosity in any of the tumors. A p53 mutation in exon 5 could be detected in the colon tumor but not in the sinonasal carcinoma, while a K-ras mutation was only present in the tumor of the inner nose. The comparative genomic hybridization method revealed different chromosomal imbalances in the different tumors. Thus, the molecular pathologic data proved the presence of 2 independent primary adenocarcinomas of the intestinal type.