Résumé : We report two boys in whom pseudohypoparathyroidism (PHP) type 1a was diagnosed at 3 and 2.5 years of age. Mild primary hypothyroidism was diagnosed prior to PHP, at the age of 1 and 15 months respectively Neonatal thyroid screening had been normal in both boys. One of them did not have the clinical features of Albright hereditary osteodystrophy (AHO) and had a severe hypocalcemia with increased serum intact parathyroid hormone (PTH) and PTH insensitivity. He had a chromosomal translocation 2; 18. The other child had several characteristics of AHO, a mild hypocalcemia and increased serum intact PTH and PTH insensitivity. He also had a nose hypoplasia which could suggest associated acrodysostosis. Both children had a decreased activity of the stimulatory guanine nucleotide-binding protein (Gs) of adenylate cyclase; only the first one had a decreased biological PTH activity in the renal cytochemical bioassay. In conclusion, although neonatal thyroid screening may be normal, hypothyroidism may develop in infancy as the first manifestation of the PHP type la. These two cases also illustrate the heterogeneity of the PHP type 1a syndrome. © 1995, The Japanese Society for Pediatric Endocrinology. All rights reserved.