False negative rates were compared in two screening modalities, physical examination with or without mammography, in an intervention study for women aged over 50 in Miyagi Prefecture. Thirty-five breast cancers were detected in 12,515 subjects who participated in the trial consisting of physical examination and mammography, whereas 44 breast cancers were detected in 50,105 subjects who received physical examination alone, so that the detection rates were 0.28% and 0.09%, respectively. Among 50,061 subjects who received physical examination alone, 8 women were diagnosed as having breast cancer within 12 months after the screening, while only one of 12,480 screenees receiving the combined modality was so diagnosed, implying false negative rates of 15.4% and 2.8%, respectively. When the screening sensitivity in the combined system was analyzed according to each single modality, the false negative rate provided by physical examination with mammography turned out to be 2.8%, significantly lower than that (33.3%) by the physical examination alone. Minimal breast cancers represented 25.7% of all screen-detected cancers in the combined modality, compared with 9.1% in the modality without mammography. The trial thus indicates that physical examination combined with mammography may be an appropriate modality for breast cancer screening in women aged over 50 on the basis of screening sensitivity.