Background:The prevalence of breast lesions (benign, precancerous and cancer lesions) in reduction mammaplasty (RM) specimens has rarely been reported in Europe and never in the Swiss population.Methods:Personal and histopathological data from 534 female patients who underwent RM were reviewed.Results:Benign and/or malignant lesions were detected in 76.2% of all patients. Benign breast lesions associated with an increased risk of developing breast cancer represented 2.8% of all lesions. Breast cancer in situ was identified in 5 (0.9%) patients. Patient age and previous history of breast cancer were risk factors for incidental breast cancer.Conclusion:The rate of incidental carcinoma in situ was higher for patients with breast cancer history. Probably due to preoperative breast cancer investigation, no occult invasive breast cancer was found in reduction mammary specimens. Therefore before RM, breast cancer evaluation should be considered for all patients, especially for those with breast cancer risk factors (e.g., patient age, personal history of breast cancer).