The objective of this study was to investigate the presence of activating mutations of the ACTH receptor gene in benign and malignant adrenocortical tumours. Genomic DNA was extracted from a variety of adrenocortical neoplasms from 16 patients and the entire ACTH receptor gene was then amplified by the polymerase chain reaction and sequenced. No mutations were detected within the coding region of the ACTH receptor gene in the 16 adrenocortical tumours studied. It is likely that mutations of the coding region of the ACTH receptor gene do not play a major role in adrenocortical tumourigenesis.