Low doses of cranial irradiation (18-24 gray) employed in the management of acute lymphoblastic leukemia may cause early or precocious puberty, predominantly in girls. To determine whether this sexual dichotomy exists at higher irradiation doses (25-47 gray), the onset of puberty was identified in 46 GH-deficient children (30 males) previously irradiated for a brain tumor not involving the hypothalamic-pituitary axis and compared with the normal pubertal standards of Marshall and Tanner. Age at irradiation was at least 2 SD below the mean age of pubertal onset in normal children. There was a significant linear association between age at irradiation and age at onset of puberty. The onset of puberty occurred at an early age in both sexes (mean, 8.51 yr in girls and 9.21 yr in boys plus 0.29 yr for every year of age at irradiation). For example, the estimated age at onset of puberty in a boy irradiated at 2 yr of age would be 9.79 yr, and that for a boy irradiated at 9 yr of age would be 11.82 yr. In the context of GH deficiency, which is usually associated with a delay in the onset of puberty, this is abnormal. At each age of irradiation, the estimated age at the onset of puberty was approximately 0.7 yr earlier in girls than boys. A similar trend was seen for bone age, which was abnormally early at the time of pubertal onset (mean, 7.39 yr in girls and 8.66 yr in boys plus 0.25 yr for every year of age at the time of irradiation). At the doses of irradiation employed in the treatment of brain tumors, radiation-induced early puberty is not restricted to girls. The clinical consequence of early puberty in the management of poor growth associated with radiation-induced GH deficiency is to foreshorten the time available for treatment with GH.