The efficacy and safety of recombinant human growth hormone (rhGH) treatment is under prospective evaluation in children with various short stature conditions. Of the 987 children enrolled up to April 1989, 836 (84.7%) had classic growth hormone deficiency (GHD) and 151 (15.3%) non-GHD. There was a predominance of idiopathic growth hormone deficiency (IGHD), with a ratio of IGHD to secondary or organic GHD (OGHD) of 2.2:1. There were more boys than girls in both the IGHD and OGHD groups. Isolated GHD was more common than multiple pituitary hormone deficiency except in some of the groups with OGHD. About half of the OGHD patients had GHD secondary to treatment for CNS tumours. Idiopathic short stature and Turner's syndrome were the most common diagnoses in the non-GHD group. The median age at onset of treatment in IGHD was 8.2 years for boys and 8.6 years for girls. The corresponding figures for OGHD were 14.0 years and 12.2 years, respectively. The height SDS for chronological age at the start of treatment was -3.0 for IGHD and slightly less for children with OGHD. Approximately one-third of the children had already reached puberty at the start of hGH treatment.