Background: Postoperative nausea and vomiting (PONV) is a common complication of pediatric anesthesia, but the overall incidence of PONV in patients undergoing adenoidectomy is unknown. The aim of this controlled study was to compare the effect of dexamethasone administration with placebo to reduce PONV in children undergoing endoscopic adenoidectomy under general anesthesia. Material/Methods: A randomized placebo-controlled study included 118 pediatric patients who underwent elective endoscopic adenoidectomy under general anesthesia. A dexamethasone-treated (0.15 mg/kg) group (Group D) (n=56) and a placebo group (Group C) (n=62) were randomly assigned. The incidence of nausea and vomiting was recorded on the day of surgery. Postoperative nausea was assessed according to illustrated Baxter Animated Retching Faces (BARF) scale. The Face, Legs, Activity, Cry, and Consolability (FLACC) scale (scores between 0-10) was used to assess pain. Follow-up was performed on the 14th postoperative day by a telephone call. Results: Overall prevalence of postoperative nausea was 25% (30/118) and postoperative vomiting was 14% (17/118). In the first 24 hours following surgery, in Group D, the incidence of nausea and vomiting was 13% and 7%, respectively; in Group C, without pharmacological prophylaxis, the incidence of postoperative nausea and vomiting was 37%, and 21%, respectively. Conclusions: A prospective controlled study in children undergoing endoscopic adenoidectomy under general anesthesia showed that dexamethasone (0.15 mg/kg) significantly reduced the incidence of PONV without increasing the risk of postoperative hemorrhage. Dexamethasone is a safe method for the prevention of PONV that may be recommended in pediatric anesthesiology.