In this study the growth curves of 229 children (145 boys, 84 girls ) with idiopathic short stature (ISS) were analysed in three ways: (1) we compared the results of longitudinal modelling by means of Karlberg's ICP model with those of a cross-sectional analysis; (2) we studied to what extent an individual changes his/her height standard deviation score (SDS) position during childhood; and (3) we constructed height velocity curves for children with ISS using Cole's LMS method, and compared these with the British references. During childhood the difference between the average longitudinal and the cross-sectional height curves was less than 1 cm and the spread was almost identical. The average change in height SDS during childhood was not different from zero, indicating that in general growth of children with ISS was well canalized. The individual change in height SDS position during childhood was within 0.6 SDS for a follow-up of 1 year, increasing to 1.9 SDS for a follow-up of 7 years. During childhood mean height velocity was about 1 cm/year lower than that of the British reference. With respect to the pubertal growth spurt the maximum height velocity took place 1 year later, and was 0.6 cm/year lower than the British reference in boys as well as girls. We conclude that spontaneous growth of children with ISS adequately described by a cross-sectional curve.