Purpose: This exploratory study examined predictive relationships between 5 types of behaviors and the trajectories of vocabulary and language development in young children with autism over 2 years. Method: Participants were 69 children with autism assessed using standardized measures prior to the initiation of early intervention (T1) and 6 months (T2), 12 months (T3), and 24 months (T4) later. Growth curve modeling examined the extent to which behaviors at T1 and changes in behaviors between T1 and T2 predicted changes in development from T1 to T4. Results: Regardless of T1 nonverbal IQ and autism severity, high scores for inattentive behaviors at T1 predicted lower rates of change in vocabulary production and language comprehension over 2 years. High scores for social unresponsiveness at T1 predicted lower rates of change in vocabulary comprehension and production and in language comprehension over 2 years. Scores for insistence on sameness behaviors, repetitive stereotypic motor behaviors, and acting-out behaviors at T1 did not predict the rate of change of any child measure over 2 years beyond differences accounted for by T1 autism severity and nonverbal IQ status. Conclusions: The results are discussed with regard to their implications for early intervention and understanding the complex factors that affect developmental outcomes.