It has been observed that various types of benign breast disease are associated to an increased risk of breast cancer. The biological significance of this association remains unclear: both benign and malignant lesions could independently have a common set of risk factors. The cellular DNA content of biopsy samples from 47 breast benign lesions was analyzed by flow cytometry. Flow cytometric measurements evidenced that 11/47 cases showed at least one aneuploid cell subpopulation. The presence of aneuploid subpopulations in benign lesions could be related to an unknown cellular alteration predisponding the developement of benign and malignant lesions independently.