Hypothalamo-pituitary function in children with optic glioma may be impaired by the tumour itself and by the high cranial radiation doses used in treatment. This study evaluates the effect of optic glioma and its treatment on patient growth and pubertal development. Twenty-one patients (13 boys, 8 girls), treated for optic glioma by cranial irradiation (45-55 Grays) at a mean age of 5.4 years, were evaluated before (n = 10) and/or after (n = 21) irradiation. Growth hormone (GH) deficiency was present in only 1 patient tested before irradiation and in all patients after irradiation. Precocious puberty occurred in 7/21 cases, before irradiation in 5 patients and after irradiation in 2 patients. The cumulative height loss during the 2 years after irradiation was 0.2 +/- 0.2 SD (m +/- SEM) in 7 patients with precocious puberty and 1.1 +/- 0.2 SD in 14 prepubertal patients (P less than 0.01). The corresponding bone age advance over chronological age, evaluated 1-3 years after irradiation, was 1.1 +/- 0.5 and -0.7 +/- 0.3 year in the two groups (P less than 0.01). The mean height loss between time of irradiation and the final height was 2.3 +/- 0.6 SD (n = 6). Primary amenorrhoea, associated with low oestradiol levels, occurred in two of the three girls of pubertal age. These data indicate that the high dose of cranial radiation used to treat optic glioma invariably results in GH deficiency within 2 years and that hGH therapy is required when GH deficiency is documented.(ABSTRACT TRUNCATED AT 250 WORDS)