Menstrual disorders are frequent in women with CAH. With the purpose to analyze the effect of the hyperandrogenism on gonadotropin secretion, we have studied 12 women with 21 hidroxilase defiency, X age 19. 3years;six had amenorrhea, 4 oligomenorrhea and 2 were eumenorrheic. One of them had never received treatment, 2 stopped treatment 2-3 years before and 9 were on corticoid replacement. Serum E2, 17OH progesterone (17 OHP), urinary 17-Ketosteroids (17-KS)and pregnanotriol (triol), and spontaneous LH and FSH levels every 20 minutes during 12 nocturnal hours (5 studies) or 4-6 diurnal hours (8 studies), were measured. Results: Three patterns of gonadotropin secretion were detected: 1)Apulsatile, n=7: X LH 1.2±0.3 IU/L; 2)Low pulsatility n=4: X LH 2.7±1.1 IU/L, X pulse amplitude (P.A.) 3.2±1.6, X pulse frecuency (P.F.) 0.23±0.08 p/hour;3) Normal pulsatility n=2 X LH 7.6 IU/L, P.A. × 4.9 IU/L, P.F. × 0.43 p/hour. No correlation was observed between gonadotropin levels and 17OHP, 17-KS or triol at the moment of study; a weak(ns)correlation was found with those values1-2 years before the study. Two patients with optimal corticoid replacement since birth, and two untreated patients presented an apulsatile gonadotropin secretion pattern. Conclusion: CAH due to 21 hydroxylase deficiency is associated with variable degrees of impaired gonadotropin secretion, even in patients with adequate corticoid treatment, suggesting an hypothalamic alteration as a consecuence of the prenatal exposure to high androgen levels.