Two hundred and thirty-six patients with idiopathic short stature (ISS) (184 m, 52 f) who presented at a mean age of 12.2 (range 2.8-17.5) years, a mean height of-2.16 standard deviation score (SDS), a mean target height (THT) of-0.27 SDS (m = 0, were reinvestigated at a mean age of 20.5 (range 18-24) years. 182 (142 m, 37 f) (67%) had reached normal adult height (AHT) while 54 (39 m, 15 f) (23%) had not. However, only 23 (17 m, 6 f) did not reach a height within their familial target. Patients were subdivided into 2 groups according to deviation from familial height target: 60 (44 m, 16 f) were considered adequate for their families (group 1), while 176 (140 m, 391) were smaller (group 2). Children in group 1 were younger and bone age (BA) was less retarded. Patients in group 1 reached their THT, this was not the case in group 2. Young age, low THT and low predicted adult height (PAH) at presentation were the factors associated with poor statural outcome, but AHT could not be predicted in individuals. In boys, PAH (Bayley-Pinneau) (0.0 SDS) exceeded AHT (-0.7 SDS), in girls, both were almost identical (-0.79, -0.77 SDS). Since most children with ISS reach an AHT within the normal range, attempts to improve AHT by means of growth-promoting therapies appear to be justified only in a minority of selected patients with ISS. Methods to improve the accuracy of individual height prognoses are needed.