Mammographic screening is one worthwhile way of reducing deaths from breast cancer among women diagnosed in ages 50-69. Our knowledge is less clear for women below 50 and above 70. Major research issues include whether by new approaches we can achieve a definitive mortality reduction in women under 50 and investigations of the efficacy of screening in the elderly. The optimal interval time has yet to be decided. When screening is taken to previously unscreened populations, effects on many parameters have to be followed, e.g., sensitivity, specificity, positive predictive value, gains, and costs. We do not as yet know what the implications of finding large numbers of women with in situ cancer are. Keeping high standards in populationbased programs also means fighting potential drawbacks: minimizing the proportion of "unnecessary" biopsies and anxiety, avoiding overtreatment of cancers with excellent prognosis, preventing false reassurance or that women with suspicious findings are left without advice. Potential drawbacks of screening are best dealt with within a team of specialists on breast cancer diagnosis and treatment. Mammographic screening has become widely accepted as one important way of reducing breast cancer deaths, and this success has been dependent on the fact that its development has been science driven. To continue to develop, the tradition of critical evaluation and unsentimental bold testing of new ideas has to be carried on. @