Pituitary tumors are discovered either incidentally by imaging studies (incidentalomas) or via evaluation of certain clinical symptoms (symptomatic tumors). In this study, we first surveyed patients with incidentalomas who underwent surgery. Cases included 62.3% non-functioning adenomas (NFPAs), 14.5% functioning adenomas, and 13.8% Rathke's cleft cysts. Next, we compared the clinical features and surgical outcomes of 145 patients whose preoperative diagnosis was NFPA (incidentalomas [n = 79] vs. symptomatic tumors [n = 66]). The patients with incidentalomas were older (59.9 vs. 55.3 years, p < 0.05) and had smaller tumors compared with the patients with symptomatic tumors (mean maximum diameter: 23.1 vs. 27.5 mm, p < 0.01). The main reason for undergoing imaging studies was headache (n = 25) in the incidentaloma group and visual disturbance (n = 46) in the symptomatic tumor group. The incidence of preoperative pituitary hormone deficiencies was lower in the incidentaloma than symptomatic tumor group (growth hormone deficiency: 37.7% vs. 66.7%, p < 0.01; gonadotropin deficiency: 19.0% vs. 39.4%, p < 0.01; adrenocorticotropic hormone deficiency: 3.8% vs. 18.2%, p < 0.01; thyroid stimulating hormone deficiency: 6.3% vs. 12.1%, p = 0.25). Postoperative pituitary function was better preserved in the incidentaloma than symptomatic tumor group (no deficiency: 58.2% vs. 28.8%, p < 0.01). The difference in postoperative complications between groups was not statistically significant (incidentalomas vs. symptomatic tumors: 21.5% vs. 19.7%, p = 0.84). In conclusion, incidentalomas were detected while smaller size and lower incidence of hormone deficiency than symptomatic tumors, and the pituitary hormones were also preserved after surgery. It is important to observe incidentalomas carefully and to judge whether to operate appropriately before they become symptomatic tumors.