Carcinomas originating in the retromolar trigone (RMT) are uncommon and characterized by early spread. Determination of mandibular invasion is significant for planning therapy and determining prognosis. For oral cavity cancers in general, CT is reasonably accurate in assessing bone invasion. However, there is a paucity of information specifically addressing the value of CT in the RMT. In this study, the records of patients with biopsy-proven RMT carcinomas treated between 1984 and 1998 were reviewed with attention to preoperative CT scans and histopathologic findings during surgery. Half of the patients who were treated with primary resection had mandibular invasion. Bone invasion was not identified radiographically in 27% of patients with preoperative CT scans. The sensitivity of CT for bone involvement in RMT cancers was 50%, with a negative predictive value of 61.1%. The positive predictive value was 91.1%. These findings suggest that CT is a useful, but potentially inaccurate, predictor of bone invasion in the RMT.