This was a prospective longitudinal design study, including four cohorts of children with CHD (born 2008-2011) who required lifelong follow-up for their CHD. Parents, who did not respond to the initial letter of invitation for their child, received a reminder by mail two months later. All children in the intervention group were recruited before three years of age. A total of 119 children (66 girls) were invited to participate and receive an oral health intervention; at baseline (below three years), at first follow-up (three years) and at second follow-up (five years). Because parents were responsible for their young children's oral health, we found no reason to exclude children with co-morbidities such as Down's syndrome, Di George syndrome, Noonan syndrome, Cornelia de Lange syndrome, Williams's syndrome and autism. According to their CHD, the children were divided in three groups; i) left-to-right shunts, e.g. atrial septal defect and ventricular septal defect, ii) obstructions, e.g. coarctation of the aorta, aortic stenosis, and pulmonary stenosis, and iii) complex heart defects, e.g. tetralogy of Fallots, transposition of the great arteries and hypoplastic left or right heart syndromes. At five years, data on oral health and oral health related background factors were compared with corresponding published data of 5-year-old children with CHD, also from Western Norway (n=67, born 2005-2007). The latter group served as controls. These children were recruited at the age of five years and had not been offered the intensive oral health intervention program received by children in the intervention group. The control group had been followed in the PDS in line with the general population of children, who are offered the first oral examination from three years of age.