The aim of the study was to investigate reasons for replacement and repair of posterior resin composite (RC) restorations placed in permanent teeth of children and adolescents attending Public Dental Health Service in Denmark.All posterior RC placed consecutively by 115 dentists over a period of 4 years were evaluated at baseline and up to 8 years later. The endpoint of each restoration was defined when repair or replacement was performed. The influence of patient, dentist and material factors on reasons for repair or replacement was investigated.A total of 4,355 restorations were placed. Replacements comprised 406 and repairs 125 restorations. The cumulative survival rate at 8 years was 84 %. Failed restorations were most frequently seen due to secondary caries (57 %), post-operative sensitivity (POS) (10 %) and RC fracture (6 %). POS was observed in 1.5 % of the evaluations and reported more often in girls and from teeth restored with a base material. Older dentists showed lower proportion of replaced restorations due to secondary caries than younger dentists.Posterior RC restorations in children and adolescents performed in general practice showed a good durability with annual failure rates of 2 %. The main reason for failure was secondary caries followed by post-operative sensitivity and resin composite fracture. A high proportion of replaced/repaired RC restorations were caused by primary caries in a non-filled surface.Secondary caries was the main reason for failure of RC in children and young adults. More teeth with post-operative sensitivity and a shorter longevity of restorations were observed when a base material was used.