Previously unsuspected pituitary tumors (incidentalomas) were analyzed in autopsies (4.8-27%) and magnetic resonance imaging (MRI) (10-37%), most of them being micro-pituitary incidentalomas (PI). However, patients with PIs sometimes had macroadenomas which may relate to previously unsuspected neurological and/or endocrine abnormalities. This study aims to establish the incidence of macro- vs. micro-PIs, the need for medical and/or surgical treatment and the neurological and endocrine dysfunction in a retrospective evaluation of patients with PIs studied over six years (1994-2000). Thirty-eight of 46 patients with PIs (22 males), aged 16-77, were followed for a mean of 3.2 years. Initial hormonal testing, ophthalmologic evaluation and MRI were repeated during follow-up. Twenty-nine (63%) of 46 patients had macro-PIs and 17 (17%) micro-PIs. Twenty-three males (75%) had macro-PIs, 10 (34.5%) with visual field defects. Consultations leading to PI diagnosis were chronic headache (28%), cranial trauma (15.3%), sinusitis (13%) and stroke (13%). Partial deficiencies of the anterior pituitary function were confirmed in 19 PIs (41.3%), with secondary hypogonadism prevailing (30%). Seven PIs (15%) were prolactinomas treated with dopamine agonists. Seventeen PIs (37%) underwent surgery. Immunohistochemical analysis showed gonadotrophinomas (30%), plurihormonal non-secreting adenomas (40%), and pituitary adenomas not reacting to any of the anterior pituitary hormone antibodies (30%). One operated macro-PI was a craniopharyngioma. Our data show a high percentage of PIs are macro-incidentalomas against expectations from necropsy and imaging studies. Most macro-PIs are found in males and are clinically non-functioning adenomas, 37% requiring surgery and hormonal substitution.