In general, mass screening for health is of doubtful value, but specific programmes like breast cancer screening could be beneficial. Breast cancer is the major cause of death in middle-aged women in many countries. Experience in Sweden shows that properly designed and performed mammography screening can reduce mortality by one-third, and lead to a better quality of life for treated cancer patients. However, if radiation causes damage proportional to the dose even at low doses, these benefits could be offset by radiogenic cancers in younger age groups (particularly under 40 yr of age). In Sweden, the direct cost of screening equals about 15 pounds sterling. Swedish authorities consider well designed screening justified. Optimization is necessary and involves design, technique, staff competence and organization. An optimized program should save one life in 100 in the screened cohort, while perhaps one life in 10,000 might be lost due to radiogenic cancers (with conventional radiation risk assumptions).