Unicameral and aneurysmal bone cysts are considered tumorlike conditions of unclear origin. The diagnosis of unicameral bone cysts is almost always based on the radiographic appearance, whereas aneurysmal bone cyst imaging may sometimes mimic a sarcomatous lesion. Several pathogenetic hypotheses [correction of hypothesis] reported in literature have been described. Classifications have been proposed to detect the activity of the cysts and to predict the prognostic behavior. The results observed with different options of treatment have been discussed.