We investigated whether the application of the downgrade criteria to supplemental screening ultrasound (US) for women with negative mammography but dense breasts can reduce the rate of Breast Imaging Reporting and Data System (BI-RADS) categories 3 to 4a without a loss of cancer detection.This retrospective study was approved by the Institutional Review Board, and the need to obtain informed consent was waived. A total of 3171 consecutive women (978 women, 1173 women, and 1020 women in the first, second, and third year, respectively) with negative mammography but dense breast who underwent radiologist-performed, hand-held supplemental screening US from March 2010 to February 2013 were included. Downgrade criteria for BI-RADS category 2 were complicated cysts ≤5?mm observed as circumscribed, homogeneous, and hypoechoic lesions and circumscribed oval-shaped solid masses ≤5?mm. Changes in the distribution of BI-RADS category, biopsy rate, and cancer detection yield over 3 years were analyzed. Performances of less-experienced (12 fellows with <2 years of experience) and experienced (3 staffs with >12 years of experience) radiologists were compared. Outcomes of initial examinations (prevalence screening) and noninitial examinations (incidence screening) were compared.Application of the downgrade criteria reduced BI-RADS categories 3 to 4a in both less-experienced (from 39.4% to 16.0%, P?