Objectives: Megestrol acetate (MA) can induce significant secondary adrenal suppression. We designed this study to determine the extent of adrenal insufficiency in cancer patients receiving MA and whether ther was any predictive factor for this. Methods: Thirty-one patients (aged 48–83 years) who were receiving MA took part in this study. Serum concentrations of TSH, ACTH, free T4, cortisol were measuresd in samples obtained at 7 AM, at baseline and 1st month. Standart ACTH (250 mg) stimulation test was performed if cortisol levels were below 18 µg/dl at any time. Results: 1 month after drug initiation, 32% of patients were accepted as adrenal insufficient. There wasn’t any correlation between the basal cortisol, ACTH levels, any biochemical parameter and overall survival. There was negative correlation between 1 month cortisol levels and survival time (p=0,04) If cortisol levels were lower at month of theraphy survival time was longer. Cox regression analysis showed that patients having lower cortisol levels at first month had 98% lower risk of death compared to patients having higher cortisol levels (p= 0,02: OR 0,12 (0,02-0,75)). Conclusions: It is important to evaluate adrenal functions especially during episodes of infection or after withdrawal of MA therapy since this may require prompt corticosteroid treatment.