Spontaneous speech samples collected from 6 autistic and 6 age- and language-matched Down syndrome controls over the course of 1-2 years were analyzed for the presence of language referring to different psychological states. Utterances containing lexical terms for desire, perception, emotion, and cognition were functionally coded to distinguish conversation uses of such terms from actual reference to mental states, and for perception terms to distinguish reference to perception from calls for joint attention. The main findings were that autistic children were comparable to the Down syndrome control subjects in their talk about desire, perception and emotion. However, they used significantly less language to call for attention and to refer to cognitive mental states. These results are discussed in relation to current theories about the nature of the psychological deficit in autism.