In this study, the characteristics of 646 patient's primary breast carcinomas, including histologic grade (HG), nuclear grade (NG), mitotic grade (MG), final grade (FG), estrogen receptor (E2R) status, and patient's lymph node status (LN) at the time of surgery were correlated with recurrence-free interval and patient survival in order to determine whether any one parameter or group of parameters serve as adequate predictors of tumor behavior and, therefore, patient's prognosis. The authors' results showed that LN, tumor size, and tumor grade were themselves significant predictors of early recurrence and breast cancer death. Each unit increase in LN or MG increased the risk of death by a factor of 1.5 and 2.0, respectively. However, prediction of time to recurrence or death was considerably more accurate when those parameters were used in conjunction, rather than individually. E2R was also significant in predicting death. MG separated patients within a single LN group or E2R group into two subsets having clinically and statistically different prognoses. It was found that patients who had negative lymph nodes and whose tumors were MG1 had a better prognosis than those with MG2,3 tumors; in these latter patients recurrence and death patterns were similar to those of patients with MG1 tumors having one to three positive lymph nodes. Similarly, whereas patients with four or more positive lymph nodes had bad prognoses, those bearing MG1 tumors tended to behave more like those with MG2,3 tumors and having only one to three positive lymph nodes.