Twenty-seven prepubertal boys and 9 prepubertal girls with constitutionally delayed growth were treated with the anabolic steroid oxandrolone for 12 months and followed until they reached final height. Sixteen boys were treated with a mean dose of 0.12 mg/kg.day [low dose (LD)] and 11 boys with a mean dose of 0.22 mg/kg.day [high dose (HD)]. The girls were treated with a mean dose of 0.1 mg/kg.day. Thirteen boys and 9 girls served as controls. On oxandrolone the mean height velocity increased from 4.0 to 8.6 (boys, LD), from 4.3 to 8.9 (boys, HD), and from 4.3 to 8.3 cm/yr (girls). The immediate posttreatment height velocity was significantly higher than the pretreatment height velocity (P less than 0.05), regardless of whether the patients had entered puberty. On oxandrolone the mean ratios of change in bone age/change in chronological age were 2.0 (boys, LD), 2.3 (boys, HD), and 2.0 yr/yr (girls) and continued to be accelerated during the 6 months after treatment. Height predictions at the onset of treatment and after 6 months off treatment were calculated by three different methods: Bayley-Pinneau (BP), Roche-Wainer-Thissen (RWT), and Tanner Mark II (T II). In the boys (LD) mean height predictions increased significantly by the methods of BP (3.3 cm) and RWT (2.9 cm), but not by the method of T II (0.6 cm). In the boys (HD) no significant change in height predictions was noted. In the girls mean height predictions remained unchanged by BP and RWT, but decreased significantly by T II (-2.5 cm). The difference between final height and initial height prediction was taken as a measure of the influence of the treatment on adult height. In all three treatment groups the difference between final height and initial height prediction, calculated with all three methods, did not differ from the control group. We conclude that oxandrolone treatment for 1 yr has no effect on adult height. In spite of this, the use of an anabolic steroid such as oxandrolone may still have value, as an increase in height velocity and an earlier onset of puberty may benefit short children suffering from psychological problems due to delay of growth and development.