Growth impairment and growth hormone (GH) deficiency are complications after total body irradiation (TBI) and hematopoietic cell transplantation (HCT). To determine the impact of GH therapy on growth, the final heights of 90 GH-deficient children who underwent fractionated TBI and HCT for malignancy were evaluated. Changes in height standard deviation (SD) from the diagnosis of GH deficiency to the achievement of final height were compared among 42 who did and 48 who did not receive GH therapy. At HCT, GH-treated patients were younger (P = .001), more likely to have undergone central nervous system irradiation (P = .007), and shorter (P = .005) than patients who did not receive GH therapy. After HCT, GH deficiency was diagnosed at 1.5 years (range, 0.8-9.5 years) for GH-treated and 1.2 years (range, 0.9-8.8 years) for nontreated patients. GH therapy was associated with significantly improved final height in children younger than 10 years at HCT (P = .0001), but GH therapy did not impact the growth of older children. Girls (P = .0001) and children diagnosed with acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), or myelodysplastic syndromes (MDS) (compared with acute lymphoblastic leukemia [ALL] or non-Hodgkin lymphoma [NHL]; P = .02) also showed more rapid growth than their counterparts. These data demonstrate that GH therapy improves the final height of young children after fractionated TBI.