Short-term cultures of fifty-two samples of fibroadenomas were cytogenetically analyzed. Thirty-three of the successfully karyotyped fibroadenomas were further investigated for the presence of amplifications in the CCND1, c-MYC and HER/2-neu genes by means of FISH analysis. Compared to carcinomas, fibroadenomas seem to have less complex cytogenetic rearrangements and limited alterations on HER-2/neu, CCND1 and c-MYC loci. A cytogenetic subgroup of fibroadenomas with hyperdiploid karyotypes and only numerical changes was observed. Amplification of CCND1 seems to play a more substantial role in benign tumor progression. These findings confirm that fibroadenomas do have genetic alterations and support the hypothesis that a fibroadenoma subset displays changes also found in carcinomas, thus indicating that patients belonging to this group might have an increased risk for subsequent breast cancer.