OBJECTIVE To critically review studies that describe patterns of care for breast cancer patients and to examine the data sources used for case identification and determining patterns of care. METHODS We searched the MEDLINE database (National Library of Medicine, Bethesda, MD) in August 2001 for studies of breast cancer care published from January 1985 to June 2001. Thirty-eight articles, describing 32 studies, met the inclusion criteria for this review. RESULTS According to the patterns of care literature, approximately 10% of women do not have an axillary lymph node dissection, 11% to 26% do not have their hormone receptor status reported, 20% do not receive radiation after breast-conserving surgery, and 30% to 70% of women with lymph node-positive breast cancer are not prescribed tamoxifen. Twenty-five (78%) of the studies relied on cancer registries for case identification. Cancer registries (47%) and the medical record (38%) were the most frequent sources of data on process of care. Twenty percent of the articles reported using more than one data source to determine patterns of care. CONCLUSIONS Although more patterns of care research has taken place in breast cancer than in any other oncologic condition, we found the available data had many limitations. These limitations highlight the challenges of quality-of-care research. To track changes in the quality of cancer care that may result from our rapidly transforming health care system, we need reliable data on the quality of current practice.