The clinically variable course of phyllode tumor with its complex histological picture--ranging from benign to malignant--poses problems for the preoperative diagnosis and, in particular, the therapeutic approach. Mammograms of 99 patients with this disease, observed and treated from 1975 to 1989, were reviewed to determine mammographic/histologic correlations useful for early diagnosis. Opacity, size, shape, margin characteristics, the presence of calcifications and radiolucent halo were determined from the mammograms. The most useful characteristics were opacity and the character of the tumor's margins. However, mammographic features alone could not distinguish phyllode tumor from fibroadenoma.