Precocius sings of puberty have been reported in some severe hypothyroid patients, suggesting the association of high secretion of gonadotropin with TSH hypersecretion.Gn-RH was evaluated in: a) 13 patients (9 females, 4 males)with long severe untreated hypoyhyroidism with precocius puberty according to bone age (range 0-6 6/12) which was 2 SD below chronological to age (range 4 5/12-14 9/12). All females had breast development, only one had pubic hair and 3/9 metrorrhagia. Males presented increased testicular size.Eight/13 patients presented enlarged sella turcica. b) 6 hypothyroid patients (1 female, 5 males) without signs of precocius puberty.Results:Group a) basal and/or serum LH responses were elevated in 12/13. Group b) basal levels of LH were elevated in 4/6. FSH showed high basal levels in 1/6.Conclusion: Primary hypothyroidism with or without signs of precocius puberty frequently presents (16/19) elevated basal levels or LH responses. Elevation of FSH is less frequent. These results suggest that TSH excess would influence gonadotropin secretion.