The mean age at menarche in 6 girls on treatment for congenital adrenal hyperplasia from infancy was 13.6 years (range 12.6–14.5 years). Menarche or regular menses did not occur until plasma testosterone concentrations were within normal limits. This was achieved using single daily dexamethasone, 0.25–0.75 mg/day. The potency of this glucocorticoid in suppressing adrenal steroid biosynthesis relative to cortisol is about 80:1. The onset of regular, ovulatory menstrual cycles, as judged by daily salivary progesterone profiles, was achieved within 2–3 years of menarche using this treatment regimen. Such patients have a good prognosis for normal fertility.