The balance between benefits and harms is delicate for cancer screening programs. By attending screening with mammography some women will avoid dying from breast cancer or receive less aggressive treatment. But many more women will be overdiagnosed, receive needless treatment, have a false-positive result, or live more years as a patient with breast cancer. Systematic reviews of the randomized trials have shown that for every 2000 women invited for mammography screening throughout 10 years, only 1 will have her life prolonged. In addition, 10 healthy women will be overdiagnosed with breast cancer and will be treated unnecessarily. Furthermore, more than 200 women will experience substantial psychosocial distress for months because of false-positive findings. Regular breast self-examination does not reduce breast cancer mortality, but doubles the number of biopsies, and it therefore cannot be recommended. The effects of routine clinical breast examination are unknown, but considering the results of the breast self-examination trials, it is likely that it is harmful. The effects of screening for breast cancer with thermography, ultrasound or magnetic resonance imaging are unknown. It is not clear whether screening with mammography does more good than harm. Women invited to screening should be informed according to the best available evidence, data should be reported in absolute numbers, and benefits and harms should be reported using the same denominator so that they can be readily compared.