The clinical history of the phyllodes tumor and its rather complex histologic patterns, ranging from benignity to malignity, often make both preoperative diagnostic procedures and the therapeutic approach very difficult to apply strictly. We reviewed the mammographic examinations of 99 patients observed and treated at the Istituto Nazionale Tumori of Milan, 1975 to 1989, looking for a mammographic-histologic correlation useful for both an unquestionable and early diagnosis and adequate excision. Many parameters were considered for each histologic type of phyllodes tumor (65 benign, 20 borderline, and 14 malignant), such as opacity, size, shape and borders of the tumor, presence/absence of calcifications inside, and radiolucent halo. The lesion was evident in all 3 projections in 85 cases (85.5%). Tumor contour was rounded in 45 instances and polycyclic in 54. Margins were distinct or mostly distinct in 81 instances (81.8%), indistinct in 11 (11.1%), and irregular in 7 (7%). The radiolucent halo was complete in 11 cases (11.1%), incomplete in 50 (50.5%), and absent in 38 (38.4%). In our experience, the most useful and characterizing mammographic parameters were tumoral borders and opacity.