In total, 524 children (335 boys, 189 girls) with idiopathic growth hormone deficiency (GHD) who had entered puberty after at least 1 year of growth hormone (GH) treatment were studied. Spontaneous onset of puberty occurred in 319 boys and 174 girls, and puberty was induced in 16 boys and 15 girls. Median chronological and bone ages at onset of spontaneous puberty were 14.8 and 13.4 years in boys, and 13.3 and 11.8 years in girls, respectively. Age at onset of spontaneous puberty was correlated to age at start of GH treatment. Puberty was induced at a median chronological age of 16.0 years in boys and 14.4 years in girls. Height velocity increased in the year before spontaneous puberty in boys and girls, and rose further to a maximum (median, 8.3 cm/year) in the first year of puberty in boys. In girls, the maximum height velocity occurred in the year before puberty (median, 6.5 cm/year). Height velocity increased in the year before spontaneous puberty in boys and girls, and rose further to a maximum (median, 8.3 cm/year) in the first year of puberty in boys. In girls, the maximum height velocity occurred in the year before puberty (median, 6.5 cm/year). Height velocity during the first year of puberty was inversely correlated to age at puberty onset (r = -0.56, p = 0.0001). After medical induction of puberty, height velocities in the first year of puberty were 5.4 and 3.4 cm/year for boys and girls, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)