Data on breast surgery from national samples of patients discharged from hospital in the United States and in England and Wales were reviewed for the years 1970-80. In the United States the rate of breast surgery increased dramatically in 1974 and 1975, but in Britain it remained constant and well below the level in the United States. In both countries the proportion of radical mastectomies declined and the proportion of less extensive procedures rose. The increase in mastectomy rates in the United States probably resulted from increased public concern about breast cancer and from the promotion of breast screening in the mid-1970s. The costs, morbidity, and early mortality associated with a higher rate of mastectomy are substantial and the advantages unclear.