We report three cases of patients with pseudohypoparathyroidism or pseudopseudohypoparathyroidism. These diseases are considered GNAS inactivating mutation syndromes that are characterized by a diversity of alterations among which a particular phenotype and specific endocrine or ossification abnormalities may be found. These patients may present with hard cutaneous nodules, which can represent osteoma cutis. The presence of these lesions in pediatric patients should prompt the dermatologist's consideration of this group of diseases when reaching a diagnosis. A multidisciplinary team of pediatricians, endocrinologists, geneticists, and dermatologists should carefully evaluate these patients.