With the advances in congenital cardiac surgery and medical management, mortality rates for congenital heart defects (CHD) have declined remarkably. As the number of CHD survivors have increased there is a growing focus on developmental morbidity. The objective of the current study is to compare symptoms of communication and social impairment in 18-month-old children with different severity of CHD with those of controls. We linked prospective data from the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health, with a nationwide medical CHD registry and identified 198 18-month-olds with CHD in a cohort of 47,692. Three groups of CHD were distinguished: mild/moderate (n= 122), severe (n= 54) and CHD with comorbidity (n= 22). Mothers reported on the child's communication and social skills by completing items from the Ages and Stages Questionnaire as part of the Norwegian Mother and Child Cohort Study. Children aged 18 months old with CHD differed significantly from controls in levels of symptoms of communication impairment (P≤ 0.0001) and social impairment (P≤ 0.0001). The largest differences were found in children with CHD and comorbidity. Children with severe CHD also showed higher levels of both symptoms of communication and social impairment. Children with mild/moderate CHD showed a small difference only in symptoms of communication impairment. Children with severe CHD and CHD with comorbidity show more symptoms of communication and social impairment compared with a large cohort at the age of 18 months. It is important to broaden the scope of inquiry to involve communication and social developmental domains.