Atrial septal defect (ASD) is a non-physiologic communication between the two atria, allowing the shunt between systemic and pulmonary circulation. Data about ASD prevalence among congenital heart disease patients (CHD) in Vietnam are still scarce. We aim to assess the trends in the prevalence of ASD patients and associated factors among CHD patients. This was a cross-sectional study, with data collected from medical records from 1220 CHD patients in Da Nang hospital from 1 January 2010 to 31 December 2015. Descriptive statistics were used to estimate the prevalence of ASD among CHD patients. Comparative statistical methods were used to compare groups and logistic regression to access associated factors with ASD. The overall prevalence of ASD among CHD patients was 18.5% between 2010 and 2015. The prevalence varied between periods, ranging between 15% and 31.9% during the period. The prevalence of ASD women among CHD (25.9%) was significantly higher than for men (16.0%). The prevalence of ASD increased gradually when the age group increased. The factors associated with increased ASD prevalence were being a female and being in an older age group. The findings suggest that targeted policy should provide more-specific health-care services of ASD for women and older patients.