Management of the axillary lymph nodes in patients with screen-detected breast cancer is controversial. Optimal treatment should combine accurate determination of node status and avoidance of unnecessary morbidity. This study attempted to determine whether axillary node status could be accurately predicted using selected criteria in women with screen-detected breast cancer. Of 223 breast cancers excised in the Greater Manchester breast screening programme, 180 were invasive and 40 of these had associated lymph node metastases. The presence of involved nodes was associated with large tumour size, high tumour grade and the absence of mammographic microcalcification. Multiple logistic regression analysis revealed that each of these three factors was independently significant. Women with a screen-detected breast cancer < 1 cm in diameter or those with grade I tumours < 3 cm (35 per cent of the total) could be spared axillary surgery with an expected reduction in morbidity and operating time.