Purpose: To compare the galactographic findings of malignant and benign disease in patients with pathologic nipple discharge and to analyze the features suggesting malignancy. Materials and Methods: In 24 patients in whom pathologic nipple discharge had occurred, the findings of preoperative galactography were correlated with those of pathology. Results: Nine of the 24 cases were malignant and the other 15 were benign. Intraductal calcification occurred in five malignant cases (56%) and two (13%) which were benign. Seven malignant cases (78%) involved the segmental ducts, and in eight (89%), the peripheral ducts below the subsegmental duct were involved. Five benign cases (33%) involved the lactiferous sinus, seven (47%) the segmental duct, and two (13%) the subsegmental duct. Distal duct dilatation occurred in four benign cases (27%), while ductal stenosis was noted in six cases (67%) and ductal distortion in seven (78%). A malignant tumor appeared as a multiple (n=5, 56%) or irregular (n=5, 56%) filling defect, and a benign tumor as a single (n=12, 80%), oval (n=6, 40%) or lobular (n=4, 27%) filling defect. Conclusion: At galactography, a malignant tumor frequently appeared as an irregular multiple intraductal filling defect in a peripheral duct. A benign tumor, on the other hand, appeared as an oval or lobular single lesion. The presence of ductal stenosis, distortion and intraductal microcalcifications not opacified by contrast material suggest possible malignancy.