This study documents changes in surgical treatment of breast cancer using data from the National Hospital Discharge Survey. All discharge records for women aged 25 years and older who received a mastectomy and had a diagnosis of breast cancer were selected for analysis. The proportion of such women discharged who received a radical mastectomy declined precipitously from 49% in 1972-1974 to 14% in 1978-1980. The proportion of women discharged who received modified radical mastectomies increased concomitantly from 29% in 1972-1974 to 64% in 1979-1980. Further, these changes in surgical practice were observed in all regions of the United States and for both small and large hospitals. The average length of hospital stay for discharged women treated surgically for breast cancer declined from 11.8 to 10.3 days between 1972-1974 and 1978-1980. About one third of this decline can be attributed to the shift toward less extensive operations.