Prognosis of 141 women with pT1 breast cancer from a defined urban area was investigated. Only one of the 47 women with a primary tumor diameter less than or equal to 10 mm in diameter (pT1a or pT1b) died from breast cancer within 5 years after the diagnosis. The 5-year survival rate corrected for intercurrent deaths of the women with pT1c cancer (from 11 to 20 mm in diameter, n = 94) was 83%; 96% in pT1cN0 and 62% in pT1cN+ cancer respectively (p less than 0.0001). In a multivariate analysis axillary nodal status and S-phase fraction determined by flow cytometry were independent prognostic factors. The excellent survival of women with pT1a or pT1b breast cancer, and women with pT1cN0 breast cancer with no axillary nodal metastases, does not support the policy of giving adjuvant treatment to all women with breast cancer.