The aim of this study was to examine the relation between symbolic play and communicative engagement among children with and without autism. Our predictions were firstly, that in moment-by-moment interactions during semi-structured interactive play with an adult, children with and without autism would tend to show shifts in meanings in symbolic play when engaged in coordinated states of joint engagement (events involving "sharing-of-meaning"); secondly, that across atypically developing participants, sharing-of-meaning would (a) correlate with scores on a standardized test of pretend play, and (b) be inversely correlated with scores on the Autism Diagnostic Observation Schedule; and finally, that participants with autism would contrast with matched developmentally delayed participants in manifesting lower levels of joint engagement, lower levels of symbolic play, and fewer shifts in symbolic meaning. Each of these predictions was borne out. The intimate developmental relation between social engagement and symbolic play appears to be important for explaining the developmental psychopathology of autism.