The estrogen (ER) and progesterone (PR) receptor status, volume corrected mitotic index (M/V index) and other classical prognostic factors were related to disease outcome in a series of 281 women with breast cancer followed up for over 8 years. The M/V index predicted recurrence only in ER+ or PR+ patients (p = 0.002-0.006). Similarly, the recurrence-free survival was related to M/V index only in ER+ (p = 0.0005) or PR+ (p less than 0.0001) patients. In survival analysis, ER+ (p = 0.0037) and PR+ (p less than 0.0001) patients were accurately divided into different prognostic groups by the M/V index, whereas in ER- and in PR-tumours the M/V index had only suggestive predictive value (p = 0.06-0.5). In N-tumours the M/V index predicted recurrence-free survival only in ER+ (p = 0.0228) and in PR+ (p = 0.0087) tumours. In survival analysis of N-tumours, the M/V index predicted cancer-related survival in ER+ (p = 0.0102) and in PR+ (p = 0.0014) tumours. In ER-/PR-, N-tumours, none of the variables tested had any prognostic value. The present results suggest that adjuvant hormone treatment might be indicated in ER+ or PR+ tumours with a M/V index greater than 10, regardless of the axillary lymph node status. The prognosis of ER+ or PR+ tumours with a M/V index less than 10 is favourable, the risk of recurrence being of the order of 15% only during the 10-year follow-up. Thus, the expensive and distressing adjuvant treatments could be omitted for these women with an inherently favourable disease outcome.