BACKGROUND: Pathological nipple discharge (PND) is a relatively common symptom of breast cancer affecting the nipple. Mammary ductscopy (MD) allows direct visualization of the ductal lumen and collection of a cytological specimen using duct-washing cytology (DWC). Herein, we clarified the diagnostic efficacy of DWC for the detection of breast cancers with PND, compared with fine-needle aspiration cytology (FNAC). METHODS: We retrospectively examined 48 patients with PND who underwent DWC by MD (ductosccopy group; histologically determined by intraductal biopsy [IDB] or surgical specimen). The results of sensitivity and specificity of DWC were compared with that of FNAC (conventional group; histologically determined by core needle biopsy). Clinicopathological factors were compared between the ductoscopy and the conventional groups. RESULTS: Of eight histologically malignant cases in the ductoscopy group, one case was cytologically judged as malignant and three as indeterminate. Sensitivity and specificity of DWC were 50.0% and 82.5%, respectively. Malignant cases were mostly solid papillary carcinomas (SPCs), and benign cases were intraductal papillomas (IDPs). In the conventional group, sensitivity and specificity of FNAC were 88.0% and 38.2%, respectively, and malignant cases were mainly invasive carcinomas of no special type. Tumors in the ductocsopy group had more favorable prognostic features than those in the conventional group. CONCLUSION: DWC has limited diagnostic value due to the high incidence of SPC, whose cytological features are indistinguishable from IDP. As DWC alone may be unreliable, comprehensive examination with IDB and MD findings is recommended.