Ninety-one patients with ameloblastoma of the mandible were studied. Among the 23 patients treated with radical surgery the recurrence rate was 8.7%, whereas the rate of 45.65% in the 68 conservatively treated patients. The prognoses of the patients treated by conservative surgery were analyzed based on the histologic and radiologic criteria of each lesion. The recurrence rate was significantly higher in the follicular type (56.8%) than in the plexiform type (32.3%). Recurrence was seen more frequently in the multilocular or soap bubble type (60.7%) than in the unilocular type (35.0%). When the recurrence rate was compared between patients aged less than 20 years and patients aged greater than or equal to 20 years, younger patients had better prognoses. It was concluded that there is a prognostic value in the histologic, radiographic, and age factors.