Chromosome analysis of a congenital or infantile fibrosarcoma from the lower left leg of a 3-week-old baby girl showed only numerical changes involving chromosomes 11, 17 and 20. As three more cases with similar combinations of trisomies of the same chromosomes have been described, this report confirms that adult and congenital fibrosarcoma are cytogenetically different and trisomy 11 may be the key-event.