The incidence of aseptic bone necrosis in 167 patients on glucocorticoid replacement therapy in our hospital was found to be 2.4% (4 patients). The diagnosis was made 16 months to five years after initiation of the therapy. A review of eight other cases reported in the literature is presented. The incidence of aseptic bone necrosis in patients on glucocorticoid replacement therapy seems much higher than might be expected. It is suggested that the dose of glucocorticoid substitution therapy be established individually at the lowest acceptable level.