To describe the fine needle aspiration cytology findings of invasive micropapillary carcinoma and correlate them with the histologic appearance. We reviewed the cytologic features of three cases of pure invasive micropapillary carcinoma in the files of Pamela Youde Nethersole Eastern Hospital from 1998 through 2000. Immunohistochemical study for epithelial membrane antigen was performed retrospectively on the cell block sections. Ultrastructural examination was also carried out on one of the cases. Two of the tumors were at pathologic stage II, and the remaining case was at stage III. Ipsilateral axillary lymph node metastases with similar morphology were seen in two of them. Cytologically, the smears were of moderate cellularity and composed of three-dimensional tumor cell balls, abortive and sometimes branching papillae, angulated tumor cell clusters, morules and occasional acini. Some of the tumor cell balls possessed scalloped borders. Focally, the tumor morules clustered together and were separated from each other by small, slitlike spaces. A small number of isolated malignant cells was also present in the background. The cell block sections showed mainly dispersed acini of tumor cells. The "reverse polarity" highlighted in histologic sections by immunohistochemical study for epithelial membrane antigen was not consistently demonstrated in the cell block material. Ultrastructural examination confirmed the focal presence of surface microvilli on the periphery of the tumor cell morules. Invasive micropapillary carcinoma of the breast possesses some subtle but distinctive cytologic features. With the help of cell block morphology and ancillary techniques, the preoperative suspicion of this rare subtype of ductal carcinoma, which carries a high propensity for lymphatic permeation, is possible.