The pretreatment growth of 1 British and 14 Swedish children with late (2-7 years) diagnosis of 21-hydroxylase deficiency (21OHD) was studied. The latter group included all patients diagnosed in Sweden after 1986. Twelve had mutations of the 21-hydroxylase gene that are generally associated with moderately severe ("simple virilizing") forms of 21OHD, one had a severe ("salt-losing") and one a mild ("non-classical") form. The British girl was followed from 4 months of age. She had grossly elevated levels of 17 alpha-hydroxyprogesterone, androstenedione and testosterone in blood, but her parents refused treatment until she was 4 years of age. None of the 15 children showed any significant increase in growth or progress of virilization until after 18 months of age. These observations indicate that growth during the first 1.5 years is not very sensitive to androgens. Thus glucocorticoid replacement during the first year of life should be kept to a minimum to avoid over-treatment.