We investigated the 2010 year prevalence of child sexual abuse (CSA) in residential and foster care and compared it with prevalence rates in the general population. We used two approaches to estimate the prevalence of CSA. First, 264 professionals working in residential or foster care (sentinels) reported CSA for the children they worked with (N = 6,281). Second, 329 adolescents staying in residential or foster care reported on their own experiences with CSA. Sentinels and adolescents were randomly selected from 82 Dutch out-of-home care facilities. We found that 3.5 per 1,000 children had been victims of CSA based on sentinel reports. In addition, 58 per 1,000 adolescents reported having experienced CSA. Results based on both sentinel report and self-report revealed higher prevalence rates in out-of-home care than in the general population, with the highest prevalence in residential care. Prevalence rates in foster care did not differ from the general population. According to our findings, children and adolescents in residential care are at increased risk of CSA compared to children in foster care. Unfortunately, foster care does not fully protect children against sexual abuse either, and thus its quality needs to be further improved.