The aim of the present study was to compare the expression of transforming growth factor (TGF) beta1 in ameloblastomas (AMs) with different risk of recurrence by immunohistochemistry. A total of 29 cases of AMs were evaluated. The tumors were divided into 2 groups: group A (10 cases) composed of unicystic and peripheral AMs, associated with a low risk of recurrence, and group B (19 cases) composed of solid AMs, associated with a high risk of recurrence. Statistical evaluation showed significant differences between groups A and B lesions, with higher values of positivity for TGF-beta1 in stromal cells in group B tumors (P = 0.0308). No statistically significant differences of immunoreactivity were found in vessels and odontogenic epithelium between the 2 groups. The increased TGF-beta1 expression in tumors with a high risk of recurrence could be explained with the fact that although TGF-beta acts as a potent tumor suppressor in the early stages of tumor progression, later it seems to enhance the invasive phenotype of the tumor.