Backgrounds â Endoscopic ultrasound (EUS)-guided placement of lumen-apposing metal stents (LAMSs) has gained popularity for the treatment of pancreatic walled-off necrosis (WON). We compared the 20-mm and 15-mm LAMSs for the treatment of symptomatic WON in terms of clinical success and adverse events. Methods â We conducted a retrospective, case-matched study of 306 adults at 22 tertiary centers from 04/2014 to 10/2018. A total of 102 patients with symptomatic WON who underwent drainage with 20-mm LAMS (cases) and 204 patients who underwent drainage with 15-mm LAMS (controls) were matched by age, sex, and drainage approach. Conditional logistic regression analysis was performed to compare clinical success (resolution of WON on follow-up imaging without reintervention) and adverse events (according to American Society for Gastrointestinal Endoscopy criteria). Results â Clinical success was achieved in 92.2âŠ% of patients with 20-mm LAMS and 91.7âŠ% of patients with 15-mm LAMS (odds ratio 0.92; P âŠ=âŠ0.91). Patients with 20-mm LAMS underwent fewer direct endoscopic necrosectomy (DEN) sessions (mean 1.3 vs. 2.1; P âŠ<âŠ0.001), despite having larger WON collections (transverse axis 118.2 vs. 101.9âŠmm, P âŠ=âŠ0.003; anteroposterior axis 95.9 vs. 80.1âŠmm, P âŠ=âŠ0.01). There was no difference in overall adverse events (21.6âŠ% vs. 15.2âŠ%; P âŠ=âŠ0.72) and bleeding events (4.9âŠ% vs. 3.4âŠ%; P âŠ=âŠ0.54) between the 20-mm and 15-mm LAMS groups, respectively. Conclusions â The 20-mm LAMS showed comparable clinical success and safety profile to the 15-mm LAMS, with the need for fewer DEN sessions for WON resolution.