This is the first study to explore lexical and grammatical development in a deaf child diagnosed with Attention Deficit Hyperactivity Disorder, Inattentive sub-type (ADHDI). The child, whose family language was Spanish, was fitted with a cochlear implant (CI) when she was 18 months old. ADHDI, for which she was prescribed medication, was diagnosed 3;6 years later. Speech samples were videotaped over the first 4 years of CI use and during a follow-up session 1 year later. Samples were transcribed according to CHAT conventions and several measures of expressive language were obtained. Receptive language was evaluated with standardized tests. Results show that while some aspects of her development seemed relatively positive (e.g., acquisition of verbal morphemes at the same auditory age as typical children), other characteristics were atypical for a CI user: (1) preference for paralexical expressions in early lexicon; (2) lexical errors in colours and other abstract words; and (3) low MLU and varied grammatical errors including disorganized discourse. Medication had a positive effect on all these characteristics, providing evidence of a link with ADHDI. This study concludes that ADHDI had a direct impact on the lexical and grammatical development in this child, as well as an indirect influence over her communicative style. More studies are needed to explore language characteristics of children with CI and ADHD. (Contains 3 tables and 2 figures.)