Background The impact of radiologists’ characteristics has become a major focus of recent research. However, the markers of diagnostic efficacy and confidence in dense and non-dense breasts are poorly understood. Purpose This study aims to assess the relationship between radiologists’ characteristics and diagnostic performance across dense and non-dense breasts. Materials and methods Radiologists specialising in breast imaging ( n = 128) who had 0.5–40 (13±10.6) years of experience reading mammograms were recruited. Participants independently interpreted a test set containing 60 digital mammograms (40 normal and 20 abnormal) with similarly distributed breast densities. Diagnostic performance measures were analysed via Jamovi software (version 1.6.22). Results In dense breasts, breast-imaging fellowship completion significantly improved specificity ( p = 0.004), location sensitivity ( p = 0.01) and the area under the curve (AUC) of the receiver operating characteristic ( p = 0.03). Only participation in BreastScreen reading significantly improved all performance metrics: specificity ( p = 0.04), sensitivity ( p = 0.005), location sensitivity ( p < 0.001) and AUC ( p < 0.001). Reading > 100 mammograms weekly significantly improved sensitivity ( p = 0.03), location sensitivity ( p = 0.001), and AUC ( p = 0.03).In non-dense breasts, breast fellowship completion significantly improved sensitivity ( p = 0.02), location sensitivity ( p = 0.04) and AUC ( p = 0.002). Participation in BreastScreen reading and reading > 100 mammograms weekly significantly improved only sensitivity ( p = 0.002 and p = 0.003, respectively) and location sensitivity ( p < 0.001 and p < 0.001, respectively). Conclusion Participating in screening programs, breast fellowships and reading > 100 mammograms weekly are important indicators of the diagnostic performance of radiologists across dense and non-dense breasts. In dense breasts, optimal performance resulted from participation in a breast screening program.