In a study of prognosis in node-negative breast carcinoma, we investigated 293 T2N0M0 patients treated by mastectomy and axillary dissection with a median follow-up of 19.8 years. The probability of surviving 20 years considering all causes of death was 41.3% +/- 3.0%. Recurrence-free survival (Kaplan-Meier estimate) was 68.6% +/- 3% at 10 years and 63.2% +/- 3.1% at 20 years. The estimated probability of cure determined by the method of Brinkley and Haybittle was 63% (95% confidence interval [Cl], 55% to 72%). Prognosis was related to primary tumor size with the best separation (P = .06) when tumors from 2.1 to 3.0 cm (33% chance of recurrence at 20 years) and from 3.1 to 5.0 cm (44% chance of recurrence at 20 years) were compared. The histologic tumor type was prognostically important. Recurrence at 20 years was not significantly different for patients with invasive duct (34%) and lobular (42%) carcinoma. Women with special types (medullary, mucinous, papillary, etc) of carcinoma had a 25% chance of recurrence. Subsequent contralateral breast carcinoma was diagnosed in 29 patients, and four of these were fatal, accounting for only 4.6% of breast carcinoma deaths. Thirty-two patients (10.9%) developed a nonmammary malignant neoplasm (NMMN) after the ipsilateral breast carcinoma, and 69% of these lesions were fatal. Although the chances of recurrence at 20 years related to tumor size and type did not differ statistically in the series, there were trends that suggest that T2N0M0 patients can be stratified into recurrence risk groups based on tumor size and histologic type. These factors should be taken into consideration in the design and analysis of clinical adjuvant therapy trials. Measures for the early detection of common NMMNs should be included in the routine follow-up of T2N0M0 breast carcinoma patients.