This prospective study was designed to assess growth response, side effects, other possible long-term effects, and final adult height in boys treated with the oral androgen, fluoxymesterone. From 1973 to 1984, eighty-two short boys (71 with constitutional delay of growth and puberty [CDGP] and 11 with genetic short stature [GSS]) were treated with daily oral doses of 2.5 mg of fluoxymesterone from 6 to 60 months. Final height assessment was made from 1989 to 1991. A group of 34 untreated boys (26 with CDGP and 8 with GSS) were also followed to assess the accuracy of the Greulich-Pyle and Bayley-Pinneau (GP-BP) and sexual maturity index height prediction methods. During treatment, each patient had a 1.7- to 2.5-fold increase in linear growth velocity. Accelerated velocity (over baseline) continued as long as the bone age was less than 14 years. No adverse androgenic effects (or undue acceleration of puberty) were observed. Final height exceeded pretreatment predictions for CDGP + GSS by 6.1 +/- 3.5 (SD) cm (GP-BP) and 5.4 +/- 3.2 cm (sexual maturity index). It is concluded that a daily oral dose of 2.5 mg of fluoxymesterone can be used to accelerate linear growth in boys with CDGP and GSS when needed to alleviate emotional problems secondary to slow growth and short stature without fear of compromising final adult height.