The strategy of early recognition and treatment of breast cancer by mass screening, practised and discussed for a number of years, is a diagnostic method whose evaluation still encounters considerable difficulties. These derive mainly from problems in the interpretation of success statistics, survival rates for a number of women, identified as »cases« who had volunteered for, or refused breast screening, or were kept as controls. With a series of biometrical arguments and very crude cost estimates, the author gets the impression that survival results would justify the increased costs that might result from mass screening.