Intentional communication is a correlate of later language in children with autism spectrum disorder (ASD). A meta-analysis on two pragmatic functions of intentional communication acts (ICAs) suggested that declarative ICAs (used to comment) are correlated with language skills, but did not provide clear evidence regarding the association of imperative ICAs (used to request) and language, nor could the relative strength of the two associations be tested adequately. In addition, the mechanism by which declarative ICAs are associated with language in children with ASD is unclear. In this study, I investigated: (1) the correlation of unprompted declarative and imperative ICAs with later expressive and receptive vocabulary; (2) the relative incremental association of declarative and imperative ICAs to predict later expressive and receptive vocabulary; and (3) the possible mediation of the relation of unprompted declarative or imperative ICAs and expressive or receptive vocabulary by parental linguistic input. The study used a longitudinal correlational design with three time periods over one year. Pragmatic function of ICAs was assessed at Time 1, parental linguistic input was assessed at Time 2, and expressive and receptive vocabulary were assessed at Time 3. The participants were 62 young children with ASD and their parents. Interrater reliability of coding for ICAs was excellent (all ICCs = 0.9). Significant correlations of unprompted imperative and declarative ICAs with later receptive and expressive language were detected. Imperative ICAs were a significantly stronger predictor of later expressive language than declarative ICAs were; no significant difference was detected in the prediction of later receptive language by declarative or imperative ICAs. Parental linguistic input mediated the relation of imperative ICAs and later receptive language; no such relation was found for declarative ICAs. Clinical implications and directions for future research are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]