Patients with Shwachman-Diamond syndrome (SDS) may exhibit a variety of hematologic manifestations including varying degrees of neutropenia. Although these patients have a known predisposition to leukemic transformation, the relationship of the predisposition to the severity of the bone marrow dysfunction or treatment is unclear. The Severe Chronic Neutropenia International Registry (SCNIR) has data from 13 patients with SDS associated with severe chronic neutropenia (SCN) which have been submitted to the SCNIR since the establishment of the registry in 1994. The age range was 10 months to 20 years at the time of registration. Eight patients received G-CSF therapy ranging from 0.4 mcg/kg/day to 10 mcg/kg/day. The duration of therapy ranged from 1 to 72 months. The patients responded to G-CSF therapy with an increase in the absolute neutrophil count (ANC before therapy, mean ± S.D., 0.43± 0.20 to 3.25 ± 2.50 109/L after therapy). Splenomegaly was reported in 3 of the 13 patients, in 1 case the finding was noted after initiation of G-CSF. Of the 13 SDS patients with data in the Registry to date, 3 patients (23%) have developed deletion of chromosome 7, one with transformation to AML. Two of these patients subsequently died and the third has survived 3 years following matched unrelated donor bone marrow transplant. No clonal chromosome abnormalities have been reported in the remaining 5 other patients with SDS who have been treated with G-CSF for varying lengths of time. Prospective studies need to be developed to better document the risk of leukemia and myelodysplastic transformation in SDS irrespective of whether the patients are receiving G-CSF.