Mc Cune-Albright syndrome, a clinical disorder characterized by sexual precocity, polyostotic fibrous dysplasia, cafe-au-lait skin lesions, and other endocnnopathies is caused by embryonic somatic mutations resulting in the substitution of histidine or cysteine for arginine at codon 201 in the α-subunit of the G-protein (Gsα). This mutation inhibits its intrinsic GTPase activity and results in the constitutively activation of adenylate cyclase. The involvement of different organs is thought to reflex the distribution of the mutation. The aim of the study was the application of a polymerase chain reaction (PCR) amplification and restriction enzyme digestion based method for mutation characterization at codon 201 of the Gsα. We studied a patient with clinical manifestations of Mc Cune-Albright syndrome presenting gonadocropin-independent precocious puberty before one year of age, typical skin spots, bone lesions, and thyroid alterations DNA was extracted from mononuclear blood cells and tissues available at surgery (skin, muscle, bone, and thyroid) A 354 DNA fragment was amplified from DNA samples of the patient and blood DNA samples obtained from a normal control. Partial NlaIII digestion of PCR fragment, marker of adenine for guanine substitution at codon 201, was observed in all samples from the patient but not from the normal control. Molecular characterization of Gsα mutations may be useful for the differential diagnosis of sexual precocity, as well as to determine its distribution by studying the mutation in potentially affected tissues.