The identification of breast ductal carcinoma in situ (DCIS) is a factor that increases 8-10 times the risk of developing invasive ductal breast carcinoma (DCI) later. In this study, we evaluated the immunoexpression of the HER2/neu oncoprotein in the DCIS cases associated with DCI, both in situ and in the invasive components. We also studied the Her2/neu immunoreactivity in the cases of DCI having no DCIS association. The positive immunoreactivity (score 3) of the HER2/neu oncoprotein was present in 29 cases of high-grade DCIS having DCI associated, corresponding to the histological types comedo, solid, comedo/solid, and micropapillary. A weak-to-moderate complete membrane staining (score 2+) was determined in five high-grade DCIS and four intermediate-grade DCIS cases, belonging to the types comedo, solid, and micropapillary. The negative immunoreactivity of HER2/neu was identified in 18 cases, most of them being of low grade and belonging to the solid and cribriform types. The invasive component of the analyzed lesions indicated a HER2/neu positive reaction in 50% of lesions having DCI associated and 17.4% of the lesions having no DCIS association. The DCIS-DCI association and the DCIS histological types that were analyzed through the HER2/immunoexpression can stand as prognostic factors for the malignant breast lesions.