Background: Percutaneous transcatheter closure (PTCC) of atrial septal defect (ASD) may convert to a long procedure. We aimed to identify predictors of prolonged procedure. Methods: Under transesophageal echocardiography and fluoroscopy guidance, 81 children with ASD underwent PTCC. Retrospectively, medical charts, echocardiographic recordings, catheterization reports and fluoroscopic films were reviewed. Demographics, echocardiographic measurements of ASD, dimensions of the device and hemodynamic data were collected. Prolonged procedure was defined as the duration from device deployment out of the delivery sheath to its release exceeding 10 minutes. A statistical model was designed using stepwise logistic regression analysis. Receiver operating characteristic curves were plotted to find the best cutoff for significant predictors. Results: The procedure was prolonged in 25 patients. By monovariate analysis, the significant predictors for prolonged procedure were smaller, and younger patients, larger ASD, smaller left atrial (LA) dimensions and device waist ratios to weight, patient's length, and LA dimensions. By multivariate analysis, the significant predictors were deficient septal rim toward superior vena cava (SVC) and device waist diameter in relation to patient's length (best cutoff: < 12 mm and > 0.13, respectively). In three cases (3.7%) the device embolized; retrospectively possibly the cause is small used device