AIm: To assess the incidence, hormonal activity and postoperative follow up of the cases that are histopathologically diagnosed as atypical pituitary adenoma (APA) in our series. Ma terIal and Methods: In this study, 13 atypical pituitary adenoma cases, by the WHO 2004 criteria, among the 146 pituitary adenoma patients operated on in our clinic between January 2009 and May 2012 by endoscopic endonasal transsphenoidal approach were included. Results: In histological studies, 133 cases were diagnosed as typical pituitary adenoma (91.1%) and 13 cases were APAs (8.9%) of which 10 were male (76.9%) and 3 were female (23.1%), ranged between 27 and 80 (mean 52.7) ages. Histopathological distribution of APAs was 9 nonsecretory adenomas (69.3%), 3 prolactinomas (23.1%) and 1 somatostatinoma (7.6%). Asymptomatic pituitary apoplexy was diagnosed in 4 cases (30.7%). Eleven cases of typical pituitary adenomas (8.2%) and 5 cases of the atypical pituitary adenomas (38.4%) were re-operated due to tumor recurrences. ConclusIon: Accurate histopathological examination shows that atypical pituitary adenoma is not a rare disease. Although it is not the only determinant, APAs are more prone to recurrence than typical adenomas. In our opinion, if total resection is not possible for the patients with APA, close postoperative follow up and additional curative therapy modalities are needed.