IMPORTANCE: Postoperative edema and ecchymosis following rhinoplasty are a cause of anxiety for both patients and physicians and can affect the cosmetic results. Corticosteroids have been used to reduce these events. OBJECTIVE: To determine whether preoperative use of dexamethasone sodium phosphate alters the occurrence of edema and ecchymosis following rhinoplasty. DESIGN, SETTING, AND PARTICIPANTS: Randomized, double-blind, placebo-controlled clinical trial at an institutional referral center among a sample of individuals with rhinomegaly. INTERVENTIONS: Patients were randomized into 2 groups. In group 1, dexamethasone was intravenously injected before surgery. In group 2, normal saline solution was intravenously injected before surgery. MAIN OUTCOMES AND MEASURES: When patients returned at 1 week after surgery, standardized photographs were obtained. The photographs were analyzed by 5 plastic surgeons who were blinded as to whether dexamethasone or normal saline solution had been injected. The plastic surgeons rated the degree of edema and ecchymosis. RESULTS: Forty-two patients participated in the study. Randomization by lottery resulted in 20 patients in group 1 and 22 patients in group 2. Group 1 showed lower rates of postoperative ecchymosis than group 2; the difference of 0.62 (P = .02) reflects less perceived ecchymosis when dexamethasone was administered. Group 1 also showed lower rates of postoperative edema than group 2; the difference of 0.68 (P = .01) reflects less perceived edema when dexamethasone was administered. CONCLUSIONS AND RELEVANCE: Preoperative use of dexamethasone reduced edema and ecchymosis at 7 days after rhinoplasty. Rigorous methods in this trial demonstrate the beneficial effect of preoperative corticosteroid administration in this surgical procedure. LEVEL OF EVIDENCE: 1.