The mammographic presentations of 300 consecutive nonpalpable breast cancers were analyzed to more clearly define the spectrum of radiographic signs needed to detect cancer at such an early stage. Clustered calcifications were the primary mammographic abnormality in 42% of cases, but only 23% demonstrated the rod, curvilinear, and branching shapes that are characteristic of malignancy. Of the 300 cancers, 39% presented as dominant masses, but only 16% showed spiculated or knobby margins typical of carcinoma. Almost 20% of the cancers were detected primarily by "indirect" mammographic signs of malignancy, such as focal architectural distortion, asymmetry, single dilated duct, and the developing density sign. To take full advantage of the capabilities of mammography, radiologists must search diligently not only for for the classic mammographic features of malignancy but especially for the more subtle and "indirect" signs that are less specific in predicting the presence of cancer.