The objective was to assess the long-term outcome of secondary alveolar bone grafting (SABG) in cleft lip and palate patients and to examine relationships between preoperative and postoperative factors and overall long-term bone graft success. The records of 97 patients with cleft lip and palate, who had secondary alveolar bone grafting of 123 alveolar clefts, were examined. Interalveolar bone height was assessed radiographically a minimum of 10 years after grafting using a 4-point scale (I-IV), where types I and II were considered a success. After an average follow-up of 16 years after SABG (range = 10.2-22.7 years), 101 of the 123 grafts (82%) were categorised as successes. Mean age in the success group was 12.1 years and 13.6 years in the failure group (p = 0.03). It was found that the success rate was significantly lower (p = 0.02) if SABG was performed after eruption of the tooth distal to the cleft. No significant differences were found with regard to the other parameters investigated. The timing of secondary alveolar bone grafting is critical with regard to the age of the patient and the stage of eruption of the tooth distal to the cleft.