The systematic mammographic evaluation of a breast mass involves independent assessments of its size, location, density, shape, clarity of margins, and interval change from prior examination. Additional fine-detail mammograms should be obtained to facilitate this analysis, especially when an equivocal interpretation is planned. Definitively benign masses (those localized to the skin, of fat density, or of mixed density) will not require more attention. Among the remaining water-density lesions, those that have an even slightly stellate appearance should be considered suspicious for malignancy; virtually all of them will undergo biopsy. Well-circumscribed masses should next be evaluated by aspiration or US examination to establish or exclude the diagnosis of simple benign cyst. Only solid and indeterminate lesions will require further evaluation, with the ultimate decision for biopsy versus mammographic follow-up depending on the probability of malignancy determined by the combination of mammographic and physical findings as well as pertinent data from the medical history.