Cytogenetic study of 18 colorectal carcinomas confirmed the extensive heterogeneity and the complexity of the karyotypic picture in this tumor.Karyotypic analysis showed that chromosomes 7 and 3 were of the highest chromosomal gaining frequencies(72%,66%) and chromosomal losses were shown in chromosome 17(50%),chromosome5(44%) and chromosome 18(33%).The structual rearrangements frequently involved were 17p(78%),5q(61%),6q,7q,8p,12q,2p,etc.A great number of marker chromosomes and polyploid chromosomes had bad prognosis relatively.According to these results,we conclude that chromosomes 17,5,and 18 may play an important role in the evolution of colorectal cancer.