OBJECTIVE To clarify the clinicopathological spectrum and biologic behavior of unicystic ameloblastomas (UA). METHODS Retrospective analysis of 33 UA was undertaken to relate clinicopathological variables to recurrence. RESULTS The clinical features of this series were in general agreement with that of the previous reports. UA tended to occur at an earlier age (mean 25.3 years), with a male predilection and predominant mandibular involvement (90.9%). Microscopically, the tumors demonstrated a generally monocystic growth pattern, with 8 being simple cystic, 10 comprising intraluminal nodules, and 15 exhibiting a conspicuous component of infiltrative tumor islands in the cyst capsule. Follow-up of 29 patients revealed 6 recurrences with an average interval of 7 years. Recurrence also related to histologic subtypes of UA, with those invading the fibrous wall having a rate of 35.7% but others 6.7%. CONCLUSIONS Despite the fact that unicystic ameloblastoma may, in general, compare favorably with its solid or multicystic counterpart in terms of clinical behavior and response to treatment, the subsets of the maxillary lesions or tumors exhibiting mural invasion could have a high risk of recurrence.