To investigate the effects of intravenous administration of dexamethasone on early postoperative cognitive dysfunction (POCD). In this prospective randomized trial, 1000 patients with facial spasm undergoing microvascular decompression (MVD) were randomly assigned to receive normal sodium (Dex-0 group, n=333), dexamethasone 0.1 mg/kg (Dex-1 group, n=333), or dexamethasone 0.2 mg/kg (Dex-2 group, n=334). Exclusion criteria included: a history of neurologic or mental disease, renal failure, active liver disease, cardiac or pulmonary dysfunction, endocrine, metabolic, or peptic ulcer disease, a history of past surgery, <6 years of schooling, inability to complete neuropsychological testing, visual dysfunction, and auditory dysfunction. Patients were also excluded at any point if additional steroid was required. Propofol and sufentanil were administered for anesthetic induction, whereas propofol and remifentanil were given for maintenance of anesthesia. A battery of 9 neuropsychological tests was administered preoperatively and the on day 5 postoperatively. A postoperative deficit was defined as a postoperative decrement to preoperative score of >1SD on any test. Patients who experienced >2 deficits were considered to have experienced early POCD. Nine hundred and fifty-four patients completed both preoperative and postoperative neuropsychological testing. Within the 3 groups: Dex-0 group, n=319; Dex-1 group, n=320 and Dex-2, n=315. POCD occurred in 71 patients (22.3%) in the Dex-0 group, in 66 patients (20.6%) in the Dex-1 group, and 99 patients (31.4%) in the Dex-2 group. POCD was significant among the 3 groups (P=0.003). Partitions of χ method was applied for multiple comparisons showing that Dex-2 group was significantly different from Dex-1 and Dex-0 groups. Administration of higher dose of dexamethasone (0.2 mg/kg) increases the incidence of POCD in the early postoperative period after microvascular decompression under general anesthesia.