We have recently demonstrated resistance to GHRH leading to GH deficiency in patients with Pseudohypoparathyroidism type Ia (Mantovani et al., J Clin Endocrinol Metab, 2003. 88: 4070-4074). The purpose of this study is to evaluate the effect of at least 1-year GH replacement in these patients. In particular, we will focus our attention on growth velocity in children affected with this disease.