This case study focuses on a bilingual, older man who spoke Polish and English and showed weaknesses on clinical measures of dichotic listening in English. It was unclear whether these test results were influenced by the participant's facility with his second language or by other nonauditory factors. To elucidate the nature of this deficit, the authors examined behavioral and electrophysiological responses during dichotic-listening tasks involving linguistic processing in both languages. A diotic (control) condition was included to examine whether nonauditory factors, such as language familiarity, memory, or decline in speed of mental processing, might explain the dichotic results. The results from this participant were compared with those obtained from a bilingual young adult who also spoke both Polish and English. Results showed a substantial left-ear deficit for the older individual on both behavioral and electrophysiological measures of dichotic listening. The pattern of results is consistent with previous findings in demonstrating that the left-ear deficit in this patient derived from an auditory-specific defect rather than from any of the extra-auditory factors associated with language facility or cognitive decline. (Contains 11 figures and 2 tables.)