Atrial septal defects (ASDs) vary greatly depending on their size, age at closure, and clinical management. This report characterizes the prevalence, complexity, and clinical management of these lesions in a statewide pediatric cohort and examines predictors for receiving closures. A 15-year Medicaid data set (1996–2010) from one state was analyzed. The selection criteria specified patients 17 years of age or younger with a diagnosis of ASD primum, secundum, or sinus venosus on one or more service visits to a pediatrician or pediatric cardiologist. During the 15-year period, ASDs represented a prevalence rate for treatment of 0.47/1000 CHDs identified, with 61 % presenting as complex lesions. Concomitant cardiac anomalies that might have a negative impact on prognosis were present including patent ductus arteriosus (26.1 %), pulmonary hypertension (3.8 %), and supraventricular tachycardia (2.4 %). Pharmacologic treatments, predominantly diuretics, were prescribed for 21 % of the cohort. Both surgical closures (6.3 %) and transcatheter closures (1.4 %) were used for ASD secundum cases, whereas surgical closures predominated for ASD primum (25.6 %) and sinus venosus (13.5 %) lesions. The postoperative follow-up period was two to three times longer for children with ASD primum or sinus venosus than for those with ASD secundum (average, ~1 year). Factors predicting the likelihood of having ASD closure were older age, having a concomitant patent ductus arteriosus (PDA) repair, treatment with ibuprofen, having two or more concomitant CHDs, and receiving diuretics or preload/afterload-reducing agents. Care of ASDs in routine practice settings involves more complications and appears to be more conservative than portrayed in previous investigations of isolated ASDs.