This study was a longitudinal examination (21 month follow-up) of language development in a pair of fraternal twins. One twin received a cochlear implant at age 20 months secondary to sensorineural hearing loss. The other twin had normal hearing. Data were obtained every 6 months following her initial cochlear implant stimulation. Both twins showed delayed expressive vocabulary skills at initial testing, but both demonstrated an expanding vocabulary over time. Receptive vocabulary of the twin with the cochlear implant at age 41 months was within the average range, but expressive vocabulary performance was delayed. When adjusted for length of implant use, expressive vocabulary performance was age appropriate. The twin normal hearing progressed faster in expressive vocabulary development and performed within the average range by age 41 months.