Oxandrolone therapy of children with uncomplicated growth retardation caused a marked increase in penile growth. The penile length percentile also showed a significant increase at the end of the therapy. Although the older boys fell into lower percentiles than the younger boys, it appears that they showed significant penile catch-up growth. Oxandrolone therapy did not appear to cause testicular growth impairment in the majority of the boys but in a few there was a temporary delay in growth.