Breast reduction mammoplasty is becoming an increasingly common procedure. A baseline mammogram is recommended after 35 years of age as the most effective method for detection of small breast cancers. A prospective study was conducted for the evaluation of the mammographic findings after reduction mammoplasty. During the last 7 years, 113 patients over 35 years of age underwent bilateral reduction mammoplasty. All patients had a preoperative mammogram. A new mammogram was obtained at 6 and 18 months after the procedure. All films were reviewed by the same two radiologists. Breast reduction was performed with the vertical bipedicle flap technique (McKissock) and the inferior pedicle technique. There were no apparent differences in the findings between the two methods. Most common findings were parenchymal redistribution in 102 (90.2%) and elevation of the nipple in 96 (84.9%), produced by a shift of the breast tissue to a lower position. Calcifications were seen in 29 (25.6%), and "oil cysts" in 22 (19.4%), caused by localized fat necrosis. A retroareolar fibrotic band was found in 23 (20.3%), from the transposed flap. Areolar thickening was observed in six (5.3%), and skin thickening in only two (1.7%), from scar tissue. Mammographic findings after reduction mammoplasty are predictable, thus preventing unnecessary biopsies and making the diagnosis of lesions unrelated to the procedure easier. All patients over 35 years of age should have a preoperative and a postoperative mammogram for future reference.