Objective To reveal the aberrations of some chromosomes in colorectal cancer (CRC) and its premalignant lesions-colorectal adenoma by using multicolor fluorescence in situ hybridization (M-FISH),so as to explore the feasibility and effectiveness of M-FISH in the early diagnosis of CRC and the evaluation of tendency of malignant transformation of the colorectal adenoma.Methods M-FISH was performed in 183 colorectal lesion biopsy specimens of 161 cases ,which included 65 adenoma tissues, 19 adenoma tissues adjacent adenocarcinoma and 99 adenocarcinoma biopsy specimens. The relationship between chromosomal aberrations and clinicopathologic parameters was also analyzed. Results The copy number gains of chromosomes 7,8,12 and 20 were 82.1%(55/67),70.1%(47/67),60.9%(56/92)and 72.8%(67/92)in the adenocarcinoma tissues,76.5%(13/17),41.2%(7/17),50%(9/18)and 72.2%(13/18)in the adenoma tissues adjacent adenocarcinomas. Chromosomal 7 and 20 presented high frequently consistent alterations in adenoma and adenocarcinoma of the same patients. Conclusion High aneuploidy rate of chromosomes 7,8,12 and 20are detected in both colorectal adenocarcinomas and adenomas. Aneuploidy rate of Chromosome 7 and 20 may be early warning signs of colorectal cancer.M-FISH may be helpful in the early diagnosis of colorectal adenocarcinomas.