The Wnt signaling pathway is involved in both normal development and tumorigenesis. Activation of the pathway results in stabilization and nuclear translocation of beta-catenin protein. Nuclear localization of beta-catenin has been used to identify tumors in which mutations in APC or beta-catenin activate Wnt signaling. We analyzed the subcellular localization of beta-catenin immunohistochemically in human fetal and postnatal tissues to identify activation of Wnt signaling during development. Nuclear beta-catenin is present in capillary endothelium, mesenchyme surrounding renal tubules, adrenal cortex, cartilage anlage, placental cytotrophoblast, and pulmonary acinar buds. These investigations suggest a defined role for Wnt signaling in human fetal development and provide a catalogue of non-neoplastic tissues with nuclear beta-catenin staining.