[Thyroid involvement in histiocytosis X]

A thyroid involvement is reported in a 10 year-old boy with histiocytosis X. It was revealed by goiter and hypothyroidism following diabetes insipidus and growth hormone deficiency. Hypothyroidism was exclusively due to the invasion of thyroid by the tumor, while the other endocrine changes were in favor of the histiocytic infiltration of hypothalamus. The exceptional feature of thyroid involvement in disseminated histiocytosis X is emphasized.