Decisions regarding the use of adjuvant therapy for breast cancer are strongly influenced by the risk of disease recurrence and death. These risks are now determined by examining the currently recognized breast cancer prognostic factors, including clinical stage, axillary nodal status, tumor size and grade, hormone receptor status, and presence of lymphovascular involvement. Newer factors are being evaluated in an attempt to more precisely define disease-related prognosis. This paper provides an overview of issues that need to be considered when analyzing studies of prognostic factors as well as a review of the currently recognized and the newer candidate prognostic factors.