OBJECTIVE To assess and develop a monocortical mandibular bone grafting procedure for reconstruction of alveolar cleft. METHODS Prospective study. METHODS Hokkaido University Hospital. METHODS Forty-two consecutive Japanese patients who had been treated for a total of 48 clefts according to a strict clinical protocol. Mean age at bone grafting was 6 years 11 months. METHODS Bone grafting was performed by harvesting lateral cortical bone plates from the symphysis and/or body and then placing them on the labial and palatal openings of the alveolar process defect. No particulate bone grafts were packed into the bony cavity. Mean follow-up after bone grafting was 37 months. METHODS Status of the grafted area and eruption of cleft-adjacent teeth were assessed prospectively using computed tomography and periapical radiography. RESULTS At 6 months postoperatively, computed tomography showed sufficient bone bridge formation at the cleft site in 85.4% of clefts. Periapical radiography showed ≥75% of the root surfaces of cleft-adjacent teeth were covered with spanning bone in 83.3% of clefts. In 92.6% of clefts in which the cleft-adjacent canine was uncovered with bone during follow-up, the canines erupted spontaneously. CONCLUSIONS Monocortical mandibular bone grafting appears extremely effective for sufficient bone bridge formation and facilitation of cleft-adjacent teeth eruption. The procedure is advantageous in that the quantity of bone required per unit volume of cleft defect is relatively reduced, and larger clefts can thus be treated.