Heterozygous loss of function mutations in human PKAR1A gene (PRKAR1A) have been identified in patients with Carney complex (CNC), an autosomal dominant familial multiple neoplasia syndrome displaying different endocrine tumors, including adrenocortical tumors, GH-secreting pituitary tumors and thyroid adenomas. Although PRKAR1A is encoded by a single gene, it is transcribed from at least two different promoters, adjacent to different first non-coding exons (1a and 1b), giving rise to alternately spliced transcripts coding for identical proteins. The separate regulation of the two distinct promoters and the presence of multiple alternatively spliced first exons suggest a complex mechanism of PRKAR1A expression regulation. In order to investigate the relative expression of the two mRNA transcripts (1a and 1b) in human adult endocrine tissues involved in the determination of CNC phenotype, we selected 17 pituitary, 20 adrenal and seven thyroid tissues from tumoral and peri-tumoral lesion samples. Expression of the two transcripts was evaluated by semi-quantitative RT-PCR and real-time RT-PCR. This study first reports that human pituitary and thyroid tissues show a similar expression of the two transcripts, whereas in adrenal tissues transcript 1b is the most abundant one.