Objectives: To compare older and younger Greek and English (U.S.) speakers on a battery of common neuropsychologic tests and to identify patterns of performance as a function of age and language. Design: Between-group experimental design. Setting: Standard clinical setting. Participants: 34 young native Greek speakers (age range, 16–46y; mean ± SD, 26.53±7.58y), 47 young English speakers (age range, 16–50y; mean, 25.62±5.8y), 26 older Greek speakers (age range, 55–90y; mean, 66.92±8.02y), and 32 older English speakers (age range, 55–92y; mean, 70.03±6.39y). Subjects were matched for sex and education. Interventions: A battery of common neuropsychologic tests administered in subjects’ native languages. Main Outcome Measures: Mini-Mental State Examination (MMSE), Rey Auditory Verbal Learning Test (RAVLT), Trail-Making Test (TMT) parts A (TMT-A) and B (TMT-B), Rey Complex Figure Test (RCFT), verbal fluency, digit span forward and backward, spatial span forward and backward, and logical memory from the Wechsler Memory Scale–III. Results: Older subjects performed 1 SD lower than younger subjects (MANOVA, α=.05) across languages. English subjects performed significantly better than Greek subjects on the MMSE (P=.001), digits forward (P=.001), digits backward (P=.002), TMT-A (P=.001), TMT-B (P=.001), semantic (P=.032), and phonemic fluency (P=.001), and logical memory (P=.001). Significant age by language interaction effects were found on the RAVLT (P=.01) and the RCFT (P=.026); older Greek subjects performed worse than the English subjects; no differences were found between younger Greek and English subjects. Conclusions: Language and culture affect neuropsychologic performance differently across age groups. Important considerations for assessing injury effects and rehabilitation efficacy will be discussed.