We measured adult heights (Ht) of 94 healthy GH-sufficient children (peak GH > 10 ng/mL, polyclonal RIA) whose Ht at presentation were more than 2 SD below the mean for chronological age, with normal weight-to-Ht ratios, normal body proportions, and pathologic growth velocity for chronological age. Group 1 (n 36, 6 females) received standardized doses (0.3 mg/kg x week) of GH (mean duration = 41 months), while group 2 (n = 58, 17 females) received no treatment. Our conclusion was that the mean final Ht SD score in the GH-treated group (-1.5) was significantly greater than in the untreated group (-2.1); P < .001. Genetic predisposition to short stature was evident in both groups: the midparental Ht SD score was -1.1 in the treated and -1.0 in the untreated group. Midparental Ht was met or exceeded by 42% of the GH-treated group but only 15% of the untreated group. Final Ht was not significantly different from predicted Ht, except from GH-treated girls, who exceeded their predicted Ht. Although the mean Ht gains (6.8 cm in girls and 3 cm in boys) were modest and variable, GH treatment provided significantly better Ht outcomes for the majority of children with idiopathic growth failure.