IntroductionAutism spectrum disorder is common in children with increasing prevalence, leading to efforts towards early identification and treatment initiation in young children. We aimed to identify the developmental trajectory of young children with an autism diagnosis and clinical factors associated with better developmental outcomes in a real-world setting.MethodsIn this study, 38 children (mean age 21.9 ± 4.7 months) who were diagnosed at < 2 years of age with autism had developmental evaluations using the Mullen Scales of Early Learning done at baseline and after 1–2 years post diagnosis and intervention initiation.ResultsIn the sample, improvements in T-scores were observed for Receptive Language (mean 26.5 to 32.0, p=0.003) and Expressive Language (mean 26.0 to 30.7, p=0.010) at the group level, while Visual Reception, Fine Motor and overall Early Learning Composite did not change significantly at follow-up. Higher baseline T-scores were consistently associated with better follow-up scores across Fine Motor, Receptive Language, Expressive Language and Early Learning Composite domains. Age at initial presentation was significantly associated with Fine Motor outcomes (β = 1.26, p=0.031) while intervention hours were not independently associated with any developmental domain outcomes in the full sample. Among children with baseline developmental delay, higher intervention hours were associated with better follow-up scores in Receptive as well as Expressive Languages and Visual Reception; this was not seen for the entire sample.ConclusionsOur results support the role of early identification and intervention for autism; however, child-level characteristics influence developmental trajectories beyond intervention hours alone.