We studied, by means of TSH nocturnal secretion and TRH test, 42 children (4.2–19.9 years) with hypothalamic pituitary disorders and 24 healthy euthyroid children (5.7–15.4 years) as control group. Patients were divided according to their serum values of FT₄ in group 1 (n = 27) with FT₄ ≥10.3 pmol/l and group 2 (n = 15) with FT₄ <10.3 pmol/l. TSH was measured by immunoradiometric assay. TSH nadir, TSH peak and TSH surge were calculated. Both groups differed significantly from control group in TSH surge values: group 1 (p < 0.05), group 2 (p < 0.01). TRH test was abnormal in 11/27 patients of group 1 and 10/15 patients of group 2. In group 1, 7 patients had normal tests, 2 had abnormalities in both tests, 9 had only TSH nocturnal surge altered and 9 showed only TRH alterations. All patients of group 2 presented thyroid axis abnormalities. In conclusion, in patients with hypothalamic pituitary disorders with low FT₄, no further investigation is required to demonstrate thyroid axis alterations, however in patients with normal FT₄, nocturnal TSH secretion and TRH test may be required to evidence thyroid abnormalities.