This prospective study evaluates the ability of a single microfocal spot magnification (1.5X) mammogram to aid in the diagnosis of isolated clustered breast microcalcifications. Of the 429 patients studied, there were 117 pathologically proved cases for which concurrent convential contact (1X) mammography resulted in an equivocal interpretation. The superior image quality of the additional magnification mammogram resulted in an equivocal interpretation. The superior image quality of the additional magnification mammogram resulted in improved visualization of microcalcifications in every instance, permitting a definitive and correct radiographic interpretation (benign or malignant) in over 70% of the cases. Microfocal spot magnification mammography as an adjunct to the conventional mammography examination can greatly improve diagnostic accuracy in the evaluation of isolated clustered microcalcifications, and should permit a substantial reduction in the number of biopsies for benign breast lesions.