Until now, no studies have investigated whether women other than those with dense breasts are suitable for adjunctive ultrasonography after negative mammography, and investigated whether all women with negative mammography are suitable for adjunctive ultrasonography.Based on the Multi-modality Independent Screening Trial in China, a total of 31,918 women aged 45 to 65 years underwent both ultrasonography and mammography. Physicians performed ultrasonography and mammography separately and were blinded to each other's findings until their interpretations had been recorded. For both ultrasonography and mammography, suspicious results and those highly suggestive of a malignancy were confirmed by pathologic examination, whereas other results were confirmed by 1-year follow-up after initial screening.Based on Breast Imaging Reporting and Data System (BIRADS) assessments, 84 (84.8%) of 99 cancers were identified on mammography (detection rate, 2.6/1000), and 61 (61.6%) of 99 cancers were identified on ultrasonography (detection rate, 1.9/1000). Integrated mammography with ultrasonography identified 94 (95.0%) of 99 cancers, with an increment of 11.9% in cancer detection rate (from 2.6/1000 to 2.9/1000) (P .05). Moreover, among women with BIRADS 3, adjunctive ultrasonography detected no cancers. All 10 additional cancers detected by adjunctive ultrasonography were from women with BIRADS 0 to 2, at a cost of 207 women with false positives. Additionally, dense breasts and benign breast disease were significantly associated with positive ultrasonography after BIRADS 0 to 2 (all P values .05).After negative mammography, adjunctive ultrasonography should only be recommended for BIRADS 0 to 2 but not BIRADS 3, especially for women with dense breasts or benign breast disease.