Background The objectives of this study were: (1) to evaluate the detectability of full-field digital mammography (FFDM) plus dual-mode digital breast tomosynthesis (DBT) and compare it with that of FFDM alone and (2) to compare the detectability of high-resolution-mode (HR mode used with 40°-angle imaging, 100-µm pixel size, and higher dose) DBT with that of standard-mode (ST mode used with 15°-angle imaging, 150-µm pixel size, and lower dose) DBT for diagnostic evaluation. Materials The local Institutional Review Board approved this retrospective study of two different sets of cases. All participants gave written informed consent. FFDM and DBT images of 471 women who were recalled were acquired between August 2013 and October 2014. HR mode and ST mode were applied to 155 breasts and 157 breasts, respectively. The cases of both modes were selected randomly. Eight radiologists interpreted the images. The detectability for recall cases and for follow cases, and area under the receiver operating characteristic curve (AUC) were calculated. Results Adding DBT to FFDM significantly increased the detectability for recall cases and AUC relative to those of FFDM alone (HR mode 8.9 %; 95 % confidence interval (CI) 5.7, 15.0 %; P  = 0.013 and 4.9 %; 95 % CI 2.1, 7.7 %; P  = 0.001; ST mode 8.3 %; 95 % CI 4.1, 12.1 %; P  = 0.007 and 2.9 %; 95 % CI 0.5, 5.3 %; P  = 0.02), whereas the detectability for follow cases did not significantly differ. The AUC increase was significantly higher in HR mode than in ST mode (1.5 %; 95 % CI 0.5, 3.7 %; P  = 0.023). Conclusion Adding HR-mode or ST-mode DBT to FFDM significantly improved the detectability for diagnostic evaluation case.