Short stature, mental retardation, and hypoparathyroidism: a new syndrome. Eight children (four boys and four girls) with extreme failure to thrive, dysmorphic features, developmental delay, hypoparathyroidism, and abnormal skeletal survey were studied. They were the products of seven consanguinous marriages, two of the patients being brothers. In the remaining six families, a further four children had affected siblings who had died in infancy. When assessed the children were aged 0.47-12.8 years; SD scores were less than -2 for height, weight, and head circumference in all patients. The children had identical facies with deep set eyes, depressed nasal bridge with beaked nose, long philtrum, thin upper lip, micrognathia, and large floppy earlobes. They were all developmentally retarded. The following abnormalities were found on investigation: hypocalcaemia in all (of whom six of seven had hypoparathyroidism), medullary stenosis and other skeletal survey defects in seven of the eight children, and reduced numbers of T cell subsets in four of four tested. We believe that these children represent a new, as yet undescribed genetically determined syndrome. 