Purpose: The purpose of this study was to evaluate the area and volume of bone available for grafting in a donor retromolar region using computed tomography (CT). Materials and Methods: Ten patients previously scanned by multislice CT were selected for evaluation. Images from partially and completely dentate patients at least 18 years of age were included in the study; those from patients with impacted or erupted third molars or intrabony lesions in the study area were not included. Computer software with appropriate tools was used to handle the images. Two calibrated observers made measurements separately. Safety margins in relation to the lingual cortex, the base of mandible, and the alveolar canal were established in each cross-section of the CTs. Measurements were done by using cross-sectional views, and the results were calculated after three-dimensional reconstruction, providing area and volume data. Results: The mean area of bone available for grafting was 8.12 cm2 (range, 0.00 to 13.60 cm2) and 8.32 cm2 (range, 0.00 to 14.30 cm2) for observers 1 and 2, respectively. Mean available bone volume for grafting was 0.79 cm3 (range, 0.00 to 1.50 cm3) for observer 1 and 0.85 cm3 (range, 0.00 to 1.60 cm3) for observer 2. Interobserver analysis showed substantial agreement. Conclusion: The retromolar region showed a wide variety of anatomic differences among patients. Three-dimensional multislice CT allows reproducible measurements of the area and volume of the retromolar region. Keywords: bone graft, computed tomography, dental implants, retromolar, volume