The aim of the study was to explore stability and change in mental health problems in Norwegian children aged 6–12 years old (n = 70) in long‐term out‐of‐home care. The children's mental health problems were assessed shortly after the placement and 7–8 years later by the caregivers and the teachers on the Revised Rutter Scales. Information on pre‐placement and placement factors were collected from the child welfare workers. At a group level the children's mental health problems had improved significantly over time according to the teachers' reports. According to the caregivers' reports, however, the children's problems were high and stable across time. Analyses aimed at detecting individual changes revealed a great variability in development according to both informants, indicating that treating the placed children as a homogenous group could be misleading. Several pre‐placement and placement variables were associated with the change in the children's mental health problems from the time of placement to the follow‐up time according to both informants' reports. However, all the predictors were accounted for by the strong effect of the children's problem scores when entering care.