Method: β-catenin immunostaining and mutational analysis of CTNNB1 gene at exons 3 and 5, when possible, were carried on a series of 19 ACT (7 malignant and 12 benign, according to Wieneke classification), from patients enrolled in the Italian Pediatric Rare Tumor (TREP) Study. Results: Immunostaining for β-catenin showed membrane/ cytoplasmic staining in 9 cases, 5 benign and 4 malignant, and nuclear staining in 1 malignant. No mutations of CTNNB1 gene were found in the 8 tumors analyzed. Conclusion: CTNNB1 gene mutations do not appear to be involved in pathogenesis of pediatric ACT. The accumulation of protein might be related to different mechanisms. Its presence in the majority of malignant ACT suggests a possible role in tumor progression.