To investigate the possible roles of E-selectin and its ligand, Sialyl Lewis X, in lymph node metastasis of invasive micropapillary carcinoma of the breast, 100 cases of invasive micropapillary carcinoma and 97 cases of invasive ductal carcinoma were analyzed immunohistochemically for the expression of E-selectin and Sialyl Lewis X, along with CD34, to measure the microvessel density of invasive micropapillary carcinoma. We found that the number of E-selectin-positive vessels was greater in invasive micropapillary carcinoma than in invasive ductal carcinoma, and it was significantly correlated with the histological grade, the number of positive lymph nodes, and the microvessel density of invasive micropapillary carcinoma. The Sialyl Lewis X expression of invasive micropapillary carcinoma was higher than that of invasive ductal carcinoma, which was also associated with lymph node metastasis. In invasive micropapillary carcinoma, the Sialyl Lewis X expression was predominantly in the stroma-facing surface of the cell clusters and the adjacent stroma, while in invasive ductal carcinoma it was largely intracytoplasmic or intercellular. These findings suggested that E-selectin and Sialyl Lewis X might play an important role in lymph node metastasis in invasive micropapillary carcinoma. The expression pattern of Sialyl Lewis X in invasive micropapillary carcinoma suggested that the reversal of cell polarity of invasive micropapillary carcinoma might be as an important factor for the morphogenesis and possibly the pathogenesis, especially their higher rates of lymph node metastasis.