Background. Adrenal insufficiency is a common complication of transsphenoidal surgery (TSS) for pituitary adenoma. It is very important to identify patients requiring glucocorticoid replacement, minimising risks of adrenal insufficiency. Aim — to assess the performance of early (3 day) post-TSS 08:00 a.m. cortisol measurement to detect and exclude secondary adrenal insufficiency. Material and methods. We selected patients undergoing TSS in our hospital during 12 months and performed a 3 day postoperative 08:00 a.m. cortisol measurement and cortisol±Synachten 6 months post-surgery. All patients received perioperative glucocorticoid replacement (first and second days postsurgery) unless basal cortisol was >10 microg/dl and cortisol after Synachten >23 microg/dl previous to surgery. We excluded patients with previous diagnosed and treated adrenal insuficiency. In patients with 3 day cortisol lower than 10 microg/dl we maintained glucocorticoid treatment until reevaluation with cortisol/Synachten 6 months post-surgery. In patients with 3 day cortisol higher than 10 microg/dl glucocorticoids were discontinued. Results. Data were reviewed from 20 patients (9 males, mean age 52,8 years), 18 with macroadenomas, 8 patients with cushing disease. Patients with adenomas no cushing: all patients with 3 day cortisol >15 microg/dl had normal cortisol/Synachten 6 months post-surgery. 2 patients with 3 day cortisol between 10 and 15 microg/dl had adrenal insufficiency 6 months postsurgery.1 patient with 3 day cortisol <10 microg/dl mantained adrenal insuficiency 6 months postsurgery. Cushing disease: all patients with 3 day cortisol >10 microg/dl had not adrenal insuficiency 6 months postsurgery, all except one with recurrence. All patients with 3 day cortisol <10 microg/dl had not recurrences, all except one with adrenal insufficiency. Conclusion. A 3 day post-TSS cortisol >15 microg/dl is a safe cutt off to discarge adrenal insufficiency. In cushing disease, a level <10 microg/dl predict a low likelihood of recurrences.