BACKGROUND: For effective postoperative antiemetic management in pediatric moyamoya disease patients receiving fentanyl based postoperative analgesia, a multimodal approach has been recommended. The uncertain efficacy of ondansetron for pediatric neurosurgical patients or the possible antiemetic effect of small dose of propofol motivated us to evaluate the preventive effect of a subhypnotic dose of propofol combined with dexamethasone on postoperative vomiting (POV), especially during immediate postoperative periods. METHODS: In a prospective observer-blind randomized controlled study, we compared dexamethasone 0.15 mg/kg alone (Group D) with dexamethasone combined with propofol of 0.5 mg/kg (Group DP) in 60 pediatric patients, aged 4-17 years, who underwent indirect bypass surgery and received fentanyl-based postoperative analgesia. Occurrence of vomiting and pain score (Wong-Baker facial score) and requirement of rescue analgesic and antiemetic were continually measured (0-2, 2-6, 6-12 and 12-24 postoperative hours). For statistical analysis, in addition to the Fisher's exact test, a generalized linear mixed model (GLMM) and the linear mixed model (LMM) for repeated measures were used for vomiting and pain scores, respectively. RESULTS: There was no statistical significance of POV incidence, requirement of rescue analgesic and pain score between the two groups at any measured intervals. The incidence of POV was 53.3% during 24 hours in both groups, and was especially 6.7% and 13.3% (P = 0.671) during 0-2 hr and 16.7% and 23.3% (P = 0.748) during 2-6 hr in group D and group DP, respectively. CONCLUSIONS: A small dose of propofol combined with dexamethasone appears ineffective to preventing POV in pediatric moyamoya patients receiving continuous fentanyl infusion.