We recently identified overexpression of the NTN4 gene in breast carcinoma effusions compared to primary carcinomas using gene-expression arrays. The objective of this study was to validate this finding at protein level and analyze the clinical role of Netrin-4 in breast carcinoma effusions. We additionally studied Netrin-4 expression and its clinical relevance in Müllerian (ovarian, peritoneal, and tubal) carcinoma effusions. Sections from 82 breast carcinomas (53 effusions and 29 solid tumors) and 57 Müllerian carcinoma effusions were stained for Netrin-4 using immunohistochemistry. Immunoreactivity was scored in carcinoma cells and analyzed for association with clinicopathologic parameters, including survival. In breast carcinoma, expression of Netrin-4 was detected in carcinoma cells in 30/53 (57%) effusions compared to 3/29 (10%) solid tumors (P < 0.001). Netrin-4 was further expressed in 31/57 (54%) Müllerian carcinoma effusions. No association was found between Netrin-4 expression in breast or Müllerian carcinoma effusions and clinicopathologic parameters, including survival. Our data provide validation on protein level of upregulated Netrin-4 expression in breast carcinoma effusions. The frequent expression of Netrin-4 in Müllerian carcinoma effusions suggests a biological role for this molecule in metastases from gynecological malignancies. Netrin-4 expression in effusions does not appear to be a predictor of disease outcome.