The female members of two different gym squads who where subject to hard training (12 to 15 hours a week), were investigated in regard to their growth parameters shortly after the beginning of intensive training and at yearly intervals thereafter. 12 of the initial 25 girls gave up training before reaching their 14th year. Only data compiled during the training period were included in the study. At the beginning of training, the gymnasts were comparable to the standard population (Zurich Longitudinal Study of Growth and Development) in regard to height and bone age: their weight was slightly subaverage. Height, growth rate, bone age, weight development and skinfold thickness remained clearly below standard values during the years of training. Due to a prolonged growth spurt during puberty, the final height and body weight were again comparable to standard values. Thelarche, pubarche and menarche were also significantly delayed; thelarche and menarche did occur, though, when the same body measurements (height, weight) as compared to the standard population were reached. FH, FSH and estradiol showed the puberty rise only after the 14th year, i.e. with considerable delay. When separately analyzing the data of the girls who gave up training before completing their 14th year, preexisting greater body measurements (including bone age) as well as more rapid development during the first years of training were found. Thus, the observed physical growth retardation is partly due to predisposition in the form of a constitutional late puberty, and is partly caused by the intensive training. A permanent physical developmental loss was not observed.