p53 status was tested in 180 patients with primary breast cancer using a yeast functional assay. Mutations were identified in 32% of cases. Only half were point missense mutations; the remainder were nonsense, insertion, deletion and splice site mutations. Twenty-two percent of mutations were located outside exons 5-8. For a median follow-up of 88 months, survival analysis showed that p53 mutation conferred a worse prognosis in the whole population and the node-positive subgroup but not in node-negative patients. p53 status, tumour size >2 cm, axillary lymph node metastasis and high histological grade were major adverse risk factors in univariate analysis. Multivariate analysis of 153 patients for whom full data were available showed that p53 status contributed prognostic information when tumour size and lymph node status were taken into account but not when histological grade was included. p53 status thus contributes only limited new prognostic information in breast cancer when established prognostic factors are taken into account. Int. J. Cancer (Pred. Oncol.) 84:587-593, 1999.