Bilateral macronodular adrenal hyperplasia (BMAH) is a rare cause of adrenal Cushing’s syndrome and was first reported in 1964 in a sporadic case. Subsequently reports of familial forms emerged after multiple family members were diagnosed with Cushing’s syndrome due to BMAH; nevertheless BMAH has mostly been considered to occur sporadically. We and others reported that preclinical BMAH could be identified on screening the relatives of apparently sporadic cases, suggesting that BMAH might be generally a familial disorder. Recently, the gene underlying BMAH has been identified. Germline mutations in Armadillo-repeat containing 5 (ARMC5) have been identified not only in patients with recognised familial BMAH, but also in apparently sporadic cases, challenging the concept of BMAH being a mainly sporadic disease. In this presentation, I will provide an overview of BMAH, discuss the discovery of the ARMC5 gene and current knowledge regarding ARMC5 function.