At Yale-New Haven Hospital (New Haven, CT) treatment of early stage breast cancer with conservative surgery and radiation therapy (CS & RT) has been utilized with increasing frequency since the 1960s. The authors have reviewed their experience with specific reference to the outcome of those patients whose breast cancer was detected on routine screening mammography. To achieve adequate follow-up, only patients treated before December 1984 are included in this analysis. Of 438 patients treated with CS & RT before December 1984, a total of 41 patients (9%) had nonpalpable lesions detected on routine screening mammography and were treated with CS & RT to the intact breast. Only two patients received adjuvant hormonal therapy and no patients received adjuvant systemic therapy. There has been only one breast failure and one death due to cancer in this group of patients resulting in actuarial survival and breast recurrence-free rates of 100% at 5 years and 92% at 10 years. These results stress the importance of routine screening mammography and raise questions regarding the role of adjuvant systemic therapy in this selected group of patients.