Forty six prepubertal boys who had constitutional growth delay were treated with oxandrolone. Mean age at the onset of treatment was 11.9 years (range 9.0-14.0) and bone age delay was 1.9 'years'. The dose of oxandrolone used was a mean of 0.05 mg/kg (range 0.03-0.18) for a mean of 0.9 years (range 0.2-3.6). Height velocity increased from a mean (SD) before treatment of 4.0 (1.0) to 7.5 (1.2) cm/year with oxandrolone. Growth rate was sustained at 7.6 (2.2) cm/year in the period after treatment. Those boys who attained a testicular volume of 4 ml or greater at the end of the treatment period had the most pronounced sustained growth acceleration. Height for bone age SD score did not alter significantly from a mean of -1.0 before treatment to -1.2 after treatment. Oxandrolone is a safe and effective treatment for prepubertal boys with constitutional growth delay.