A case study of Denis, a prelingually hearing-impaired boy who has bilateral severe-to-profound sensory neural hearing loss, is presented. Separate analyses of his spoken and signed language were made, and the change in the relationship between the two modalities was examined. At age 15 months, when Denis began producing signs (MLU 1), he used sign almost exclusively; vocalization was rhythmic and intonational but not meaningful. Eight months later, his expressive language development had changed dramatically: He understood and used speech most of the time, using sign only with new and unfamiliar material. By age 3 years, his oral language compares with that of hearing children of the same age. The case study has practical implications for the education of prelingually hearing-impaired children: Signs have become vehicles for attaching meaning to sounds.