To investigate clinical characteristics, metabolic parameters and follow-up findings of subjects with incidentally discovered adrenal tumors. 376 consecutive subjects who have been evaluated since 2002 were included. Initial radiological examination was CT. Hormonal evaluation included 8.00 a.m. cortisol, DHEA-S, ACTH and in hypertensive subjects, plasma renin activity, and serum aldosterone. Urinary free cortisol (UFC), urinary normetanephrine, and metanephrine were measured. Overnight 1 mg dexamethasone suppression test was performed. Radiological evaluation was performed at 6th and 12th months and annually in subsequent visits. Hormonal evaluation was performed 6 months after the initial visit and annually in subsequent visits. Additionally, patients were evaluated for the development of Type 2 diabetes mellitus, hypertension, hyperlipidemia, and metabolic syndrome in 6-month intervals. Mean age of the participants was 54.7 ± 13.1. Female subjects were more commonly affected (70%). CT was the most frequent radiological intervention that discovered adrenal masses (57%). The vast majority of the participants (85.6%) had benign adrenal adenomas. Primary adrenocortical malignancy was detected in 4 subjects (1.1%). Subjects with adrenal adenomas had significantly smaller tumor diameters (P ≤ 0.001 vs. other tumors). Sensitivity and specificity of 40 mm as a cut-off value in the differentiation of adrenal gland malignancies from benign tumors was 73.3 and 54.8%, respectively. Most of the adrenal adenomas were non-functioning (73.5%). Subclinical Cushing syndrome (sCS) was detected in 12.5%. The overall prevalence of Type 2 diabetes mellitus, hypertension, hyperlipidemia, and metabolic syndrome was 18.4, 54.9, 59.6, and 48.1%, respectively. They were significantly more common in middle-aged and elderly subjects. During 24 months follow-up 10.2% of adenomas featured increase in tumor diameter and 2.06% developed sCS. Young subjects featured more stable tumor diameter and hormonal status. Most of the incidentally discovered adrenal tumors were non-functioning adrenal adenomas. Clinically overt hormone hypersecretion syndromes were mainly shown in young subjects, while adrenal gland malignancies and sCS were more common in older ages. Mass enlargement and development of subclinical cortisol secretion were not rare and observed especially in middle-aged and elderly subjects. Metabolic derangements were common; however, a possible independent association between adrenal adenoma and metabolic problems need to be elucidated with prospective studies.