Background: Although prior studies evaluated the role of EUS and EGD for drainage of pancreatic pseudocysts, there are no randomized trials that compared the technical outcomes between both modalities. Objective: To compare the rate of technical success between EUS and EGD for transmural drainage of pancreatic pseudocysts. Study design: A prospective randomized trial. Setting: A tertiary-referral center. Patients: Those with a history of pancreatitis and symptomatic pancreatic pseudocysts that measured greater than 4 cm in size who were referred for endoscopic transmural drainage. Patients with pancreatic abscess or necrosis were excluded. Main Outcome Measurements: Technical success was defined as the ability to access and drain a pseudocyst by placement of transmural stents. Complications were assessed at 24 hours and at day 30. Treatment success was defined as the complete resolution or decrease in size of the pseudocyst to ≤2 cm on CT in association with clinical resolution of symptoms at 6 weeks of follow-up. Results: Thirty patients were randomized to undergo pseudocyst drainage by EUS (n = 15) or EGD (n = 15) over a 6-month period. Of the 15 patients randomized to EUS, drainage was not undertaken in one, because an alternative diagnosis of biliary cystadenoma was established at EUS and was excluded (after randomization) from analysis. The mean age of the patients was 47 years; 62% were men (18/29). Except for their sex, there was no difference in patient or clinical characteristics between the 2 cohorts. Although all the patients (n = 14) randomized to an EUS underwent successful drainage (100%), the procedure was technically successful in only 5 of 15 patients (33%) randomized to an EGD (P < .001). All 10 patients who failed drainage by EGD underwent successful drainage of the pseudocyst on a crossover to EUS. There was no significant difference in the rates of treatment success between EUS and EGD after stenting, either by intention-to-treat (ITT) analysis (100% vs 87%; P = .48) or as-treated analysis (95.8% vs 80%; P = .32). Major procedure-related bleeding was encountered in 2 patients in whom drainage by EGD was attempted; one resulted in death and the other necessitated a blood transfusion. No significant difference was observed between EUS and EGD with regard to complications either by ITT (0% vs 13%; P = .48) or as-treated analyses (4% vs 20%; P = .32). Technical success was significantly greater for EUS than EGD, even after adjusting for luminal compression and sex (adjusted exact odds ratio 39.4; P = .001). Limitation: Short duration of follow-up. Conclusions: When available, EUS should be considered as the first-line treatment modality for endoscopic drainage of pancreatic pseudocysts given its high technical success rate. © 2008 American Society for Gastrointestinal Endoscopy.