The two French registries for childhood disabilities, which cover the departments of Haute-Garonne (RHE31), Isère, Savoie, and Haute-Savoie (RHEOP), are specifically tasked with systematically recording children diagnosed with autism spectrum disorder (ASD) no later than the calendar year in which they turn 8. This study provides an estimate of the prevalence and characteristics of children included in the two registries, born between 1995 and 2010 and diagnosed with ASD no later than between 2003 and 2018. From the cohort of children born in 1995–97 to that of 2007–09, the prevalence of ASD rose from 2.3 to 7.7 per 1,000 and from 3.3 to 5.6 per 1,000 for the RHE31 and RHEOP, respectively. Among boys born between 2007 and 2009, the prevalence reached 12.3 per 1,000 for the RHE31 and 9.0 per 1,000 for the RHEOP. For both registries, there was a significant decrease in the proportion of children with associated intellectual disability. However, the proportion of children with ASD presenting comorbidities remained high. In conclusion, these results confirmed an increase in ASD diagnoses among 8-year-olds, with a prevalence of 8 to 10 per 1,000 for children born in 2010, along with more precise diagnoses and a greater number of children without associated intellectual disability. This registry-based surveillance system provided an updated prevalence estimate that is fully comparable to recent European estimates for the same age groups.