The extent of vocabulary depends on the success of rehabilitation in hearing, language and speech. In hearing impaired and deaf children, it is important to select the optimum technical device-hearing aid or cochlear implant. This study was performed on 30 children with hearing aids or cochlear implants using the Test of Expressive Vocabulary for Children Aged 3-6 years (Kiese-Himmel and Kozielski). The development of vocabulary was recorded over 12 months. The results were analysed dependent on the degree of hearing loss, age at primary diagnosis, duration of treatment and kind of hearing aid used. These were compared with the reference data from a normally hearing population. Cochlear implant users had better language development than hearing aid users despite a lower grade of hearing loss in the hearing aid group. In general, the extent of the expressive vocabulary was less in hearing impaired children than in the reference population. However, in terms of hearing age, the language development of some cochlear implant users was similar to that of normal children.