This study investigates the linguistic competence of an autistic child by means of her bedtime soliloquies. It suggests the usefulness of such monologues as a diagnostic tool and addresses the question of the interrelationship between echolalia and language development. Three bedtime soliloquies of an eight-year-old echolalic autistic child are analyzed along the dimensions of echolalia versus prepositional speech, types of ungrammatically produced, and analysis of connected discourse. The results are compared with those of a normal child reported earlier in the literature. The present analysis demonstrates the difficulties in the judgment of prepositional versus echolalic speech. The types of ungrammaticality were found to be useful indicators of apparent differences between the acquisition process in the normal and the autistic child. They revealed that the autistic child may use specific linguistic strategies only minimally utilized by the normal child. The discourse analysis points up additional differences as well as similarities in the way the autistic subject organizes her utterances in connected discourse. It also shows that the autistic child has specific but limited linguistic competence. It is hypothesized that the autistic subject acquires more functional, useful language by a process of gradually breaking down echolalic patterns. In terms of therapy, these findings would support the use of echolalia as a basis for language training.