The authors prospectively assessed the effectiveness of requests for immediate additional evaluation or biopsy made on the basis of the interpretation of abnormal findings on screening mammograms. In 1,125 screening mammograms obtained in asymptomatic women referred by physicians, the findings in 63 (6%) were interpreted as requiring additional imaging or biopsy. Written reports were sent, and in all cases the office of the referring physician was notified directly by phone. Physicians were periodically contacted if no follow-up had been performed to resolve the questioned abnormality. In the first 2.5 months, no action had been taken in 40 of 63 (63%) of the recommendations. After additional calls, this diminished to 10 of 63 (16%) at 3.5 months, but at 4.5 months four of 63 (6%) patients had not undergone the recommended additional studies. These results suggest the need for development of systems to ensure prompt action in patients with abnormal findings at mammographic screening.