Short stature in the adult patient with congenital adrenal hyperplasia (CAH) is commonly seen, even among patients in excellent adrenal control during childhood and puberty. In this study we examine the effect of GH therapy on height prediction in children with both CAH and compromised height prediction. Leuprolide acetate, a GnRH analog (GnRHa), was given to patients with evidence of early puberty. GH (n = 12) or the combination of GH and GnRHa (n = 8) was administered to 20 patients with CAH while they continued therapy with glucocorticoids. Each patient in the treatment group was matched according to age, sex, bone age, puberty, and type of CAH with another CAH patient treated only with glucocorticoid replacement. The match was made at the start of GH treatment. Of the 20 patients, 12 have completed 2 yr of therapy. After 1 yr of GH or combination GH and GnRHa therapy, the mean growth rate increased from 5 +/- 1.9 to 7.8 +/- 1.6 cm/yr vs. 5.4 +/- 1.7 to 5 +/- 2 cm/yr in the group not receiving GH (P < 0.0001). During the second year of treatment, the mean growth rate was 6 +/- 1.6 vs. 4.2 +/- 2.1 cm/yr in the group not receiving GH (P < 0.001). The height SD score for chronological age in the treatment group at the end of 1 and 2 yr of treatment improved significantly more than the nontreatment group (P < 0.01). A similar improvement in the height SD score for bone age was found in the treatment group after 1 (-1.4 +/- 0.9 vs. -1.7 +/- 0.9; P < 0.0001) and 2 yr of therapy (-0.67 +/- 0.68 vs. -1.7 +/- 1.2; P < 0.0004). The mean predicted adult height improved from 159 +/- 11 (baseline) to 170 +/- 7.5 cm (after 2 yr of therapy) closely approximating target height (173 +/- 8 cm). All patients continued the hydrocortisone treatment. In patients with CAH and compromised height prediction, treatment with GH or the combination of GH and GnRHa results in an improvement of growth rate and height prediction and a reduction in height deficit for bone age.