British Columbian provincial practice guidelines (PPGs) have recommended breast-conserving surgery (BCS), axillary node dissection, and radiation therapy following BCS for specific subgroups of breast cancer patients. Patient-, disease-, and physician-specific factors associated with these therapies were investigated in nonmetastatic invasive breast cancer patients. Temporal trends in BCS and physicians' experiences with PPGs were also examined. Sources of data for patient, disease, treatment, and treating physician factors included medical records, source documents, and the British Columbia Medical Directory for 967 nonmetastatic invasive breast cancer patients diagnosed in British Columbia in 1995. BCS utilization among 496 patients with pathologically node-negative breast cancer (NNBC) was compared to earlier British Columbian data. Family physicians and surgeons were surveyed in 1997 regarding their experience with PPGs. 57% of "ideal" candidates received BCS; 87% of patients received axillary node dissection; and 95% of women treated with BCS also received radiation therapy. Tumor size, tumor location, and extent of ductal carcinoma in situ (DCIS) were associated with BCS use; age, tumor size, and tumor location were associated with axillary node dissection; and age alone was associated with radiation therapy following BCS. Fifty-four percent of NNBC patients received BCS in 1995, compared to 44% in 1991, with increases seen in most patient-, disease-, and physician-specific comparisons. The increase in BCS, and high proportion completing radiation therapy, are encouraging and may be due in part to greater exposure to PPGs.