Introduction - The objective of this study is to describe, using data from the French Registry of Childhood Disabilities (RHEOP), the prevalence and characteristics (associated disabilities, risk factors, care) of severe intellectual disabilities (SID) in children across three French departments (Isère, Savoie, Haute-Savoie). It also allows for a comparison of characteristics and care based on the presence or absence of associated severe impairments and an analysis of temporal trends in SID and Down syndrome. Methods - The analysis focused on 7-year-old children with severe intellectual disabilities residing in the three departments. Results - Analysis of RHEOP data shows that intellectual disability in children is a common severe neurosensory disability, with a prevalence rate of 3 per 1,000 children residing at age 7 in one of the three Alpine departments. In nearly half of the cases, this intellectual disability is associated with another severe disability, psychiatric disorder, or severe motor impairment; in such cases, the proportion of children with severe or profound developmental delay is higher. One-third of children with severe intellectual disability have severe or profound developmental delay (IQ < 35). The cause of ID remains difficult to identify and is more often prenatal in children with isolated ID. At age 7, 40% of children are enrolled in mainstream schools but only 15% of them are in regular classrooms, often in preschool and/or receiving support from a classroom assistant. Schooling is highly dependent on the type of associated disability. Conclusion - Analysis of trends over time shows that, for children with isolated SLI, the prevalence rate has remained stable for the past twenty years, whereas the prevalence rate for children with Down syndrome has been decreasing. (R.A.)