Background: Adult patients with intellectual disabilities often strongly resist the anesthetic administration for dental procedures. This study aimed to evaluate the effect of midazolam premedication in improving the cooperation level of patients who are likely to be combative and irritated during general anesthesia (GA) induction. Methods: The patients who had received dental treatment under ambulatory GA for more than two times were included. And we selected 13 patients total that needed physical restraint or ketamine IM prior to induction at the first GA, and were prescribed midazolam tablet (7.5-15 mg) at the following GA. We reviewed pre-anesthetic records and anesthesia records, and evaluated cooperative levels of patients (4 levels scale) during anesthesia induction and recovery time retrospectively. Results: All 13 patients (Male 11, Female 2) had severe mental disabilities. The average age of the patients was 24 ${pm}$ 7 (13-37) years and their average weight was 58 ${pm}$ 16 (34-91) kg. At the first GA, 10 patients needed physical restraint prior to induction (level 3). And 3 patients were so poorly cooperative that the induction procedure was performed after intramuscular injection of ketamine (level 4). But after the midazolam intake, 7 patients were willing to receive the anesthetic induction (level 1, 2), and 6 patient needed physical restraint (P < 0.05). There were no statistical differences in the duration of general anesthesia and postoperative recovery. Conclusions: Oral intake of midazolam was effective in improvement of cooperation without any complications.