The authors present information of a group of 63 patients (60 women and 3 men) treated in 1976-1998 where supernumerous aberrant or accessory mammary gland tissue was found. The diagnosis in the majority of the patients was based on histological examination. The tissue of an aberrant mammary gland is subject to the same physiological influences as the mamma proper and can be affected by the same pathological processes--benign and malignant. This is the reason why the authors recommend early extirpation.