Purpose: Prelingual deaf children with cochlear implants show lower digit span test scores compared to normal-hearing peers, suggesting a working memory impairment. To pinpoint more precisely the subprocesses responsible for this impairment, we designed a sequence reproduction task with varying length (two to six stimuli), modality (auditory or visual), and compressibility (sequences with more or less regular patterns). Results on 22 school-age children with cochlear implants and 21 normal-hearing children revealed a deficit of children with cochlear implants only in the auditory modality. We observed no deficit in the visual modality and no deficit in the ability to detect and use regular patterns to improve memorization. Conclusion: These results suggest that the working memory deficit of children with cochlear implants is explained by an impairment in the processing, encoding, and/or storage of the auditory and lexical information, as opposed to a global storage deficit or an inability to use compressibility strategies to improve memorization.