The following case illustrates pseudoinfilanation of fibrous stroma of the breast by duetal carcinoma in situ (DCIS) subsequent to fine-needle aspiration (FNA). Epithelial clusters in the fibrous stroma mimicked small foci of influating carcinoma. However, features compatible with FNA effect include the presence of collections of hemosiderin-ladenmacrophages in the surrounding stroma, luminal fibrin and blood clots in ducts with DCIS, and the similarity of the epithelial clusters in the stroma to those trapped within the fibrin and blood clots. The lack of a desmoplastic response precluded the diagnosis of inflinating carcinoma. Invasion was nor found in either the biopsy or the mastectomy specimen. Awareness of a previous FNA or other needing procedure may prevent an crroncous histologic diagnosis of inflinating carcinoma. Fine-needle aspiration or instrumentation effect should be considered whenever the histologic findings are not classic for invasive carcinoma.