Morphological variation in left atrial appendage (LAA) and structural mismatch between LAA ostia and LAA closure (LAAC) devices can result in incomplete closure and peri-device leak (PDL) post-LAAC. Prior data had suggested that PDL of ≤5 mm was not clinically relevant, but recent larger datasets have demonstrated that any PDL after LAAC is associated with a higher thromboembolic risk. But these data were largely obtained at a time before LAAC To determine the incidence and impact of PDL in a large single-center experience. We performed retrospective analysis of 650 consecutive patients who underwent LAAC (with Watchman/Watchman FLX; Boston Scientific Inc). PDL presence was assessed from the 1-yr follow-up TEEs or cardiac CT scans (1-yr imaging is routine in our practice). A multivariable analysis was conducted to assess for predictors of PDL including age, gender, congestive heart failure, chronicity of AF (paroxysmal vs non-paroxysmal) and the LAAC device iteration (initial generation vs FLX). Between 3/2015 - 12/2021, a total of 650 patients underwent LAAC at our center: age 75.8±8.9 yrs, male 64%, CHA2DS2-Vasc 4.2±1.4. One-year TEE/CT imaging identified PDLs in 146 (22.5%) patients, with PDL size being 2.2±1.9 mm. The only multivariable predictor of PDL was the presence of non-paroxysmal AF (adjusted OR 1.9, 95% CI: 1.3- 2.9, p = 0.002). During the study follow up period, there were a total of 35 (5.4%) strokes. The presence of any PDL at 1-yr was associated with a higher stroke risk (OR: 4.9, 95% CI 2.2-10.6, p < 0.001) than in the absence of PDL. PDLs are not uncommon after LAAC, and when present, were associated with a substantially higher risk for thromboembolism. Non-paroxysmal AF predicted PDL, perhaps because of adverse LAA remodeling in these patients. Our findings raise the question of the potential utility of PDL closure/coiling or reinitiating anticoagulation (perhaps low dose) in patients with persistent PDL after LAAC.