Background We describe calendar time trends of patients with simple congenital heart disease. Methods and Results Using the nationwide Danish registries, we identified individuals diagnosed with isolated ventricular septal defect, atrial septal defect, patent ductus arteriosus, or pulmonary stenosis during 1977 to 2015, who were alive at 5 years of age. We reported incidence per 1 000 000 person-years with 95% CIs, 1-year invasive cardiac procedure probability and age at time of diagnosis stratified by diagnosis age (children 18 years), and 1-year all-cause mortality stratified by diagnosis age groups (5-30, 30-60, 60+ years). We identified 15 900 individuals with simple congenital heart disease (ventricular septal defect, 35.2%; atrial septal defect, 35.0%; patent ductus arteriosus, 25.2%; pulmonary stenosis, 4.6%), of which 75.7% were children. From 1977 to 1986 and 2007 to 2015, the incidence rates increased for atrial septal defect in adults (8.8 [95% CI, 7.1-10.5] to 31.8 [95% CI, 29.2-34.5]) and in children (26.6 [95% CI, 20.9-32.3] to 150.8 [95% CI, 126.5-175.0]). An increase was only observed in children for ventricular septal defect (72.1 [95% CI, 60.3-83.9] to 115.4 [95% CI, 109.1-121.6]), patent ductus arteriosus (49.2 [95% CI, 39.8-58.5] to 102.2 [95% CI, 86.7-117.6]) and pulmonary stenosis (5.7 [95% CI, 3.0-8.3] to 21.5 [95% CI, 17.2-25.7]) while the incidence rates remained unchanged for adults. From 1977-1986 to 2007-2015, 1-year mortality decreased for all age groups (>60 years, 30.1%-9.6%; 30-60 years, 9.5%-1.0%; 5-30 years, 1.9%-0.0%), and 1-year procedure probability decreased for children (13.8%-6.6%) but increased for adults (13.3%-29.6%) were observed. Conclusions Increasing incidence and treatment and decreasing mortality among individuals with simple congenital heart disease point toward an aging and growing population. Broader screening methods for asymptomatic congenital heart disease are needed to initiate timely treatment and follow-up.