Increasing interest has been focused on DNA ploidy, hormone receptor status and tumour size as prognostic factors in node-negative breast cancer. We analysed these factors in patients operated on for primary invasive breast cancer between January 1981 and December 1987 in a prospective study of 248 women with no involved axillary nodes and 188 women with positive nodes followed until 15 April 1989. Oestrogen or progesterone receptor negativity, aneuploidy and tumour diameter exceeding 20 mm were studied as negative prognostic signs in life table analyses and Cox proportional hazards models of corrected survival. Corrected survival decreased with increasing number of negative signs. Three to four signs yielded a statistically significant, two- to threefold higher risk than the others. Survival estimates by life table analyses differed by 20% at 5 years. In the whole group, women with three or four negative factors had a relative risk of dying from their disease more than twice that of the others. Women with no involved nodes and with three or four negative factors had a risk of dying from breast cancer similar to that of node-positive women with fewer than three.