Two quantitative methods, Confidence Profiles and CAN*TROL, are used to analyze evidence and estimate the health and economic consequences of adding annual mammography to annual breast physical examinations in asymptomatic women aged 40 to 49 years who are at average risk for breast cancer. Such women have about a 128 in 10 000 chance of having breast cancer in the next ten years and about an 82 in 10 000 chance of dying of such a cancer. Adding annual mammograms to annual breast physical examinations each year during that age decade would reduce the probability of death to about 60 in 10 000, a reduction of about 26%. Screening would increase the expected lifetime of a woman destined to get breast cancer between ages 40 and 49 years by about 3.5 years. Ten years of screening with mammography in that age decade carries a risk of radiation-induced cancer of about one in 25 000 and a risk of a surgery recommendation for a lesion that is not cancer of about one in ten. If 25% of the women in this age group in the United States were screened every year, breast cancer mortality in the year 2000 would be decreased by about 373 deaths. In 1984 dollars, the cost of screening, workups, and continuing care in the year 2000 would be about $408 million. Treatment costs would be decreased by about $6 million, leaving a net increase in costs in the year 2000 of approximately $402 million (1984 dollars).