We report the international experience in outcomes after related and unrelated hematopoietic transplantation for infantile osteopetrosis in 193 patients. Thirty-four percent of transplants used grafts from HLA-matched siblings, 13% from HLA-mismatched relatives, 12% from HLA-matched, and 41% from HLA-mismatched unrelated donors. The median age at transplantation was 12 months. Busulfan and cyclophosphamide was the most common conditioning regimen. Long-termsurvival was higher afterHLA-matched sibling compared to alternative donor transplantation. There were no differences in survival after HLAmismatched related, HLA-matched unrelated, or mismatched unrelated donor transplantation. The 5- and 10-year probabilities of survival were 62% and 62% after HLA-matched siblingand42%and39%after alternative donor transplantation (P5.01 andP5.002, respectively). Graft failurewasthemostcommon cause of death, accounting for50%of deaths after HLA-matched sibling and43%of deaths after alternative donor transplantation. The day-28 incidence of neutrophil recovery was 66% after HLA-matched sibling and 61% after alternative donor transplantation (P5.49). The median age of surviving patients is 7 years. Of evaluable surviving patients,70%are visually impaired;10%have impaired hearing and gross motor delay. Nevertheless, 65% reported performance scores of 90 or 100, and in 17%, a score of 80 at last contact. Most survivors >5 years are attending mainstream or specialized schools. Rates of veno-occlusive disease and interstitial pneumonitis were high at 20%. Though allogeneic transplantation results in long-term survival with acceptable social function, strategies to lower graft failure and hepatic and pulmonary toxicity are urgently needed.