AIM To review factors resulting in a false-negative outcome or delayed cancer diagnosis in women recalled for further evaluation, including ultrasound, after an abnormal screening mammogram. MATERIALS AND METHODS Of 646,692 screening mammograms performed between 1 January 1995 and 31 December 2004, 34,533 women were recalled for further assessment. Nine hundred and sixty-four interval cancers were reported in this period. Forty-six of these women had been recalled for further assessment, which specifically included ultrasound evaluation in the preceding 24 months, and therefore, met the inclusion criteria for this study. Screening mammograms, further mammographic views, ultrasound scans, clinical findings, and histopathology results were retrospectively reviewed by two consultant breast radiologists. RESULTS The interval cancer developed in the contralateral breast (n=9), ipsilateral breast, but different site (n=6), and ipsilateral breast at the same site (n=31) as the abnormality for which they had recently been recalled. In the latter group, 10 were retrospectively classified as a false-negative outcome, nine had a delay in obtaining a biopsy, and 12 had a delay due to a non-diagnostic initial biopsy. Various factors relating to these outcomes are discussed. CONCLUSION Out of 34,533 women who attended for an assessment visit and the 46 women who subsequently developed an interval breast cancer, 15 were true interval cancers, 10 had a false-negative assessment outcome, and 21 had a delay to cancer diagnosis on the basis of a number of factors. When there is discrepancy between the imaging and histopathology results, a repeat biopsy rather than early follow-up would have avoided a delay in some cases. A normal ultrasound examination should not deter the radiologist from proceeding to stereotactic biopsy, if the index mammographic lesion is suspicious of malignancy.