Children with autism spectrum disorder (ASD) and structural language impairment (LI) may be at risk of more adverse social-developmental outcomes. We examined trajectories of early social competence (using the Vineland-II) in 330 children aged 2-4 years recently diagnosed with ASD, and compared 3 subgroups classified by: language impairment (ASD/LI); intellectual disability (ASD/ID) and ASD without LI or ID (ASD/alone). Children with ASD/LI were significantly more socially impaired at baseline than the ASD/alone subgroup, and less impaired than those with ASD/ID. Growth in social competence was significantly slower for the ASD/ID group. Many preschool-aged children with ASD/LI at time of diagnosis resembled "late talkers" who appeared to catch up linguistically. Children with ASD/ID were more severely impaired and continued to lag further behind.