Aspiration specimens from 12 patients with histologically documented ductal carcinoma-in-situ (DCIS) of the breast (seven patients) or DCIS with minute foci of stromal invasion (five) were evaluated. Five patients presented with palpable masses, 1.5-4.0 cm, and four patients presented with localized thickening, associated with nipple erosion and discharge in two of them. One patient had nipple inversion, and one patient had bilateral nipple discharge. In one patient, no apparent abnormality of the breast was present. Mammography was either suspicious for or strongly suggestive of carcinoma in 10 patients and negative in two. Aspirates from all patients were composed of fragments of atypical ductal epithelium and numerous single epithelial cells. In nine cases, the smears were hypercellular and similar to aspirates of typical invasive ductal carcinoma. Calcifications were present in six cases. In four of these, associated tumor necrosis was evident. Cytologic features separating DCIS patients from those showing minimal stromal invasion or common types of invasive ductal carcinoma (IDC) were not identified. We conclude that fine-needle aspiration cytology of DCIS is identical to that of IDC. If preoperative radiotherapy or chemotherapy is considered in the management of invasive breast carcinoma, cutting-needle biopsy for confirmation of tumor invasion is necessary.