A case of factitious hypercortisoluria due to the presumed addition of glucocorticoid to the urine collections is presented. The discrepancy between urine and blood steroid hormone levels first suggested that the patient had tampered with the urine collections. Plasma steroid hormone levels were normal, whereas the urinary free cortisol level fluctuated in a totally random fashion. Urinary 17-hydroxycorticosteroid and urinary free corticosterone levels were normal. Partition chromatography of the urine indicated that the cortisol immunoactivity coeluted with authentic cortisol. This study illustrates the value of multiple urinary and plasma steroid determinations, especially urinary or plasma corticosterone measurements, in suspected cases of factitious Cushing's syndrome.