CHILD (congenital hemidysplasia, ichthyo-sis, and limb defects) syndrome is a rare, usually sporadic disorder associated with unilateral distribution of ichthyosiform skin lesions, limb defects, punctate calcifications of cartilaginous structures, and visceral anomalies. CHILD syndrome shares some manifestations with X-linked dominant Conradi-Hunermann syndrome (CDPX2), although the skeletal defects and skin lesions in CDPX2 are bilateral and asymmetric. Because CDPX2 patients have abnormal 8-dehydrosterol metabolism caused by mutations in 3-hydroxysteroid-8, 7-isomerase, we measured plasma sterols in a patient with CHILD syndrome and found levels of 8-dehydrocholesterol and 8 (9)-cholestenol increased to the same degree as in CDPX2 patients. Subsequently, we identified a nonsense mutation in exon 3 of the patient’s 3-hydroxysteroid-8, 7-isomerase gene. We speculate that at least some cases of CHILD syndrome are allelic with CDPX2 caused by 3-hydroxysteroid-8, 7-isomerase deficiency. Am. J. Med. Genet. 90: 328–335, 2000© 2000 Wiley-Liss, Inc.