A cytogenetic study of 8 cases of anal canal cancer, including I cloacogenic and 7 squamous-cell carcinomas, was performed. All tumors exhibited chromosomal abnormalities. A rearrangement involving the long arm of chromosome 11 was seen in all instances, and, with the exception of the i (11q) found in one tumor, all the observed rearrangements resulted in a deletion of the distal segment. Rearrangements of chromosome 3, detected in 6 tumors, led to a deletion of the short arm in 5 cases. The association of these 2 deletions may characterize the anal canal carcinoma, the smallest common deleted segments being distal to 11q22 or q23 and 3p22.