Background: Little is known about the stability of individual restricted and repetitive behaviors (RRBs) in children with autism spectrum disorders (ASD) (i.e., how commonly behaviors are lost or improve and how often they are acquired or worsen over time.) There is evidence that ‘repetitive sensorimotor’ (RSM) behaviors (e.g., motor mannerisms) follow different developmental trajectories than ‘insistence on sameness’ (IS) behaviors (e.g., rituals).

Objectives: We examine the stability of individual RRBs over time in children with ASD, and which factors are associated with stability.

Methods: Data were collected as part of a longitudinal study of toddlers referred for possible autism. There were 214 participants in the first cohort, 192 of whom were referred because of concerns about ASD. The nonspectrum developmental disorder (DD) referral group consisted of 22 developmentally delayed children who had never been referred for or diagnosed with autism. At each wave, children completed a battery of cognitive and diagnostic measures, and parents completed the Autism Diagnostic Interview-Revised. At ages 2, 5, and 9, each child was assigned a consensus best-estimate clinical diagnosis of autism, pervasive developmental disorder-not otherwise specified, or a nonspectrum developmental disorder.

Results: Once children with ASD had a particular RSM behavior, they were likely to continue having it, and children who did not have the behavior often acquired it. However, these behaviors often improved in children with higher nonverbal IQ (NVIQ) scores and/or milder ASD. Many children who did not have IS behaviors at a young age acquired them as they got older, whereas children who had these behaviors sometimes lost them. Trajectories of IS behaviors were not closely related to diagnosis and NVIQ.

Conclusions: Individual RRBs show different patterns of stability in children with ASD, based partly on the ‘subtype’ they belong to. Young children with low NVIQ scores often have persistent RSM behaviors.