Bone involvement is a common finding in Cushing's syndrome. The actions of corticosteroids on bone have been studied quite intensively but only a few studies of bone histomorphometry in this syndrome have been published. In this paper we present histomorphometric measurements of bone activity in 7 patients with a postoperative reevaluation in two. The results show irregular alterations on histomorphometric parameters with an increased bone resorption and decreased bone formation rate. After surgery the abnormalities changed towards normal.