Five children (four boys, one girl) with Noonan's syndrome were treated with growth hormone for a mean of 2.9 (range 1.8 to 4.6) years. Treatment was commenced at a mean age of 3.9 (range 2.5 to 6.0) years. After one year of treatment, height velocity SDS increased from a mean of ‐2.1 (range ‐4.1 to ‐ 0.3) to a mean of +3.1 (range +2.0 to +3.5). Subsequently, height SDS increased significantly from ‐3.3(range ‐4.2 to ‐2.2)to ‐2.4(range ‐3.3 to ‐ 1.6). Although in all patients a marked decrease in height velocity was observed in the following years of treatment, compared to the first year, height SDS continued to improve in comparison to pretreatment (mean height SDS in the third year for four patients was ‐2.1) (range ‐3.1 to ‐ 1.4). In the four patients who had completed their second year of treatment, height SDS for bone age had increased from ‐1.8 (range ‐ 2.8 to ‐ 09)