The aim of this study was to assess the preoperative alveolar cleft volume and the adequacy of bone fill and bony bridge postoperatively using Cone Beam Computed Tomography. This study was carried out on six patients with unilateral alveolar cleft with age ranging from 9 to 20 years old, average 15.8 years complaining of unilateral alveolar cleft. The patients were selected from those attending the Outpatient Clinic of the Departments of Oral and Maxillofacial Surgery and Orthodontics, Faculty of Oral and Dental Medicine, Cairo University. CT scans of six patients with unilateral clefts were taken immediately preoperatively and six months postoperatively. The patients underwent surgery using iliac crest bone grafts. The data was transferred to the work station of the navigation system. Using the I-CAT machine and Simplant view 12.03 software, the defect at the alveolar clefts and volume of the bone grafts were determined in each case. Three-dimensional models were created showing the amount of bone immediately preoperatively and six months postoperatively. Results: The mean and standard deviation values of alveolar cleft volume of all patients were 0.92 ± 0.27 (cm3) and 0.62 ± 0.41(cm3) pre- and post-operatively, respectively. The mean and standard deviation values of bony bridge were 38.8 ± 24.3 % with a minimum of 0% and a maximum of 69%. The mean and standard deviation values of bony bridge % were 64.5 ± 6.4 % and 26 ± 17.6 % after secondary and late secondary alveolar bone grafting surgery, respectively. In conclusion, Volume assessments using cone beam computed tomography and simplant software is a reproducible and practical method to assess alveolar cleft defect and the outcome of secondary alveolar bone grafting.