Objective To summarize the characteristics of etiological factors in patients with different genders and ages who were diagnosed as adrenal incidentaloma (AI). Methods Clinical data of 1173 AI patients admitted to Chinese PLA General Hospital from July 1994 and July 2013 were collected and retrospectively analyzed. Results For both males and females, non-functional adrenal tumors had the highest proportion. The proportion of pheochromocytoma was obviously higher in the males than in the females (P＝0.001), but that of subclinical Cushing’s syndrome was just the opposite (P＝0.005). The incidence of metastatic adrenal carcinoma was significantly higher in the male than in the female patients (P＝0.006). Non-functional adrenal tumors still occupied the highest proportion among the patients at different ages. With aging, the proportion of the lesions was also elevated (P＝0.028), but that of pheochromocytoma was declined (P＜0.001). There was no significant difference in etiological factors among the male patients at different ages, but the proportion of non-functional adrenal tumors was increased among the female patients with aging (P＝0.005), with those over 70 years old taking the highest. The proportion of pheochromocytoma was reduced with aging (P＜0.001). Conclusion There are significant gender- and age-related differences in etiological factors in AI patients.