This study examined the stability of scores on the ADI-R from pre-school to elementary school age in children with autism spectrum disorders (ASD). Participants were 35 children who, at T1, all had a clinical diagnosis of ASD. On initial assessment (mean age 3.5 years; SD 0.6 years), all met ADI-R algorithm criteria for autism. ADI-R assessments were repeated at follow up (FU; mean age 10.5 years; SD 0.8 years). Changes in ADI-R total, domain and ADI-R algorithm item scores were assessed. Twenty-eight children continued to score above the ADI-R cut-off for autism at FU, although significant decreases in ADI-R domain and item scores were also found. In conclusion while classification of children according to ADI-R criteria generally remained stable between pre-school and elementary school age, many children demonstrated significant improvements in symptom severity.