Background: More than half of women present nipple discharge during reproductive age. Case: This case is about a 36 years old woman with unilateral spontaneous hyaline nipple discharge associated with breast pain. The study of scintimammography was compatible with multifocal proliferative lesion in situ. It was performed cytological smear of nipple discharge. It was paucicellular smear represented by cluster of ductal cells in three-dimensional design with hyperchromatic nuclei in the presence of myoepithelial cells. Red cells and signs of necrosis were not observed. The diagnosis of in situ ductal carcinoma was confirmed in biopsy and mastectomy specimen through the expression of calponin in myoepithelial cells at immunohistochemistry. It is known that the cytological examination of nipple discharge has low sensitivity and specificity. However, it is an easy and inexpensive procedure. Suspicious or positive results, may be important for guidance workup of patients in order to perform earlier diagnosis of malignancy. Conclusion: this case demonstrates that in situ ductal carcinoma can be characterized by positive nipple discharge, and cytology sample is an important tool for the diagnosis of suspicion of malignancy and further diagnostic investigation.