Ultrastructural alterations of the endocrine glands in patients with Tay-Sachs disease have so far not been reported. Clinical observations of precocious puberty in baby girls with Tay-Sachs disease prompted an endocrine study which revealed an increase of either plasma luteinizing hormone or follicle stimulating hormone, or both, as well as an increase in 24-hour urinary estradiol, estriol, and testosterone levels. The ultrastructure of the pituitary, pineal, adrenal, and ovarian glands, and the cerebral cortex and hypothalamus from one of the children was studied in order to find a morphologic explanation for this phenomenon. In the anterior and posterior portions of the pituitary gland, cerebral cortex, and hypothalamus, typical Tay-Sachs lipid bodies were observed, whereas membranous lipid bodies were noted in the pineal gland. Adrenal and ovarian involvement were absent. The relationship of these organs to the precocious puberty, however, remains uncertain. The alteration in these endocrine glands is further evidence of the widespread distribution of these lipids, and suggests that the metabolic defect is ubiquitous in tissues of patients with Tay-Sachs disease.