In recent years, some studies of postoperative computed tomography evaluations of secondary bone grafting into the alveolar cleft have been reported. Here we report a study of volumetric evaluation and prognostic factors for bone bridge formation after secondary bone grafting into the alveolar cleft using computed tomography. In 60 patients with unilateral cleft lip and palate (30 with unilateral cleft lip and alveolar ridge: UCLA, 30 with unilateral cleft lip and palate: UCLP), we performed computed tomography scanning pre- and post-operatively. We calculate bone bridging ratio from the bone defect volume and evaluated prognostic factors for it. The median bone bridge ratio was 83.6% and 66.3% in UCLA and UCLP, respectively. Both univariate and multivariate analysis indicated that the presence of cleft palate and preoperative bone defect volume were statistically significant prognostic factors. The type of tooth inducted into the alveolar cleft or its state of eruption were not related to prognosis.