Growth of 92 Finnish patients with 21-hydroxylase deficiency (21-OHD) was analyzed retrospectively to study growth both before the diagnosis and during glucocorticoid substitution therapy. The patients were divided into two groups: those diagnosed at infancy (56 patients) and those diagnosed after the age of 1 y (36 patients). Birth lengths of those boys and girls diagnosed at infancy were greater than the national mean birth lengths (p < 0.001). Mean relative length diminished from +0.8 SD score (SDS) at birth to -1.0 SDS by the age of 1 y. Adult height was -1.0 SDS (159.9 cm) for women and -0.8 SDS (173.6 cm) for men. The difference from national mean height was significant only for women (p = 0.026). Mean relative weight during childhood correlated negatively with adult stature (r = -0.620; p = 0.006). In the group of children diagnosed later in their childhood, growth was already accelerated at infancy from +0.2 SDS at birth to +0.7 SDS by the age of 1 y (p = 0.023). The final height of girls diagnosed later in childhood was within normal limits (-0.5 SDS; 162.1 cm), whereas it was low in the corresponding group of boys (-2.1 SDS; 165.3 cm). Our data show increased mean birth length in babies with early diagnosis of 21-OHD and growth acceleration at infancy in children diagnosed later in their childhood, reflecting the growth accelerating effect of adrenal hyperandrogenism early during fetal life and infancy. To improve final height in patients with 21-OHD, lower doses of hydrocortisone should be used at infancy, and special attention should be paid to boys diagnosed later in childhood.