From the National Cooperative Growth Study database 106 patients (53 boys) with myelomeningocele who were treated with recombinant human growth hormone (GH) at 56 centers were identified. Eighty-one patients (41 boys) were prepubertal at enrollment. The mean pretreatment growth rate (GR) in these prepubertal patients was 4.5 +/- 3.7 cm/yr, and the mean height SD score was -4.0 +/- 1.2. The maximal stimulated GH level was less than 10 micrograms/L in 71% of these patients and less than 7 micrograms/L in 49%. The mean chronologic age was 6.5 +/- 2.9 years, and the mean height age was 3.7 +/- 1.7 years. After GH treatment the year 1 GR in those who remained prepubertal was 8.5 +/- 3.3 cm/yr, a significant increase over baseline (p < 0.01). This increase was sustained through year 4 and remained significant through year 3 (p < 0.01). The height SD score showed sustained significant improvement through year 4, to -2.2 +/- 1.4 (p < 0.001). The GR and SD score for stature improve with GH treatment in children with myelomeningocele.