Objectives To address the benefits of double and arbitration reading regarding tumour detection rates, percentage of in situ tumours, and number (of patients) needed to send for expert reading (number needed to treat; NNT) for one additional tumour finding. Methods QuaMaDi is a quality assured breast cancer diagnosis programme; with two-view mammography (craniocaudal, mediolateral oblique) and, in case of breast density ACR 3 or 4, routine ultrasound imaging; and with independent double reading of all images. A consecutive sample of symptomatic women, i.e. women at risk for breast cancer, women aged 70 and above, and/or women with preceding BI-RADS III findings, was analysed. Results 28,558 mammograms were performed (mean age of women: 57.3 [standard deviation: 12.3] years). Discordant findings were present in 3,837 double readings and were sent for arbitration reading. After histopathological assessment, 52 carcinomas were found (thereof 32% in situ). These carcinomas accounted for 1.8 tumours per 1,000 examinations in the total cohort and increased the tumour detection rate up to 16.4/ 1,000. The NNT in discordant cases was 74. Conclusion Double and arbitration reading appears to be a useful tool to ensure the quality of early detection of breast lesions in symptomatic women during indication-based, standardised mammography. Key Points • Quality assured breast cancer diagnosis is feasible outside organised screening structures. • Double and arbitration reading is beneficial for populations ineligible for screening. • Double and arbitration reading increases the tumour detection rate. • Double and arbitration reading increases the percentage of in situ cancers.