Noonan syndrome (NS) is an autosomal dominant disorder that can be difficult to diagnose. Growth retardation is a consistent feature, however, and although children are not typically growth hormone (GH) deficient, a minority may have suboptimal GH levels. An ongoing multicentre study examining the safety and efficacy of GH therapy in NS showed increases in height standard deviation scores (SDS; p < 0. 0001) and height velocity (p < 0.0001) after 12 months of GH at pharmacological doses. There was no increase in mean maximal cardiac left ventricular wall thickness during the 12-month treatment period. Long-term follow-up data covering 3 years of GH therapy showed sustained increases in height SDS and height velocity compared with baseline (p < 0.02). Further large and appropriately controlled studies of high-quality design are essential to further our understanding of NS and to establish the long-term safety and efficacy of GH.