The previous mammograms of 148 patients with screen-detected breast cancer were examined at Breast Test Wales, Cardiff. Women who showed 'minimal signs' on previous screen mammograms formed the study group. Age, average size of tumour, tumour characteristic, grade and lymph node status were compared to a control group, which had normal previous mammograms. Student t-test and chi-square test were used, with P-value < 0.05 being taken as significant. Images were interpreted first by a senior registrar and then by a breast radiologist who was blinded to the results of current mammograms.