Background: Pulmonary hypertension (PH), recently redefined as mean pulmonary arterial pressure >20 mm Hg (PH ₂₀ ), may be observed in patients with atrial septal defects (ASD). We aimed to determine the effect of preprocedural PH ₂₀ status on outcomes among patients undergoing ASD closure. Methods: Study population was selected from a retrospective registry of adult patients who underwent percutaneous ASD closure from 1998 to 2016 from a single center and had right heart catheterizations during the procedure. The clinical registry was linked to administrative databases to capture short- and long-term outcomes. Results: We included a total of 632 ASD closure patients of whom 359 (56.8%) had PH ₂₀ . The mean follow-up length was 7.6±4.6 years. Patients with PH ₂₀ were older (mean age 56.5 versus 43.1 years, P <0.001) and a higher prevalence of comorbidities including hypertension (54.3% versus 21.6%, P <0.001) and diabetes (18.1% versus 5.9%, P <0.001) than those without PH. In a Cox proportional hazards model after covariate adjustment, patients with PH had a significantly higher risk of developing major adverse cardiac and cerebrovascular events (heart failure, stroke, myocardial infarction, or cardiovascular mortality), with hazards ratio 2.45 (95% CI, 1.4–4.4). When applying the prior, mean pulmonary arterial pressure ≥25 mm Hg (PH ₂₅ ) cutoff, a significantly higher hazard of developing major adverse cardiac and cerebrovascular events was observed in PH versus non-PH patients. Conclusions: ASD patients with PH undergoing closure suffer from more comorbidities and worse long-term major adverse cardiac and cerebrovascular events outcomes, compared with patients without PH. The use of the new PH ₂₀ definition potentially dilutes the effect of this serious condition on outcomes in this population.