The relationship between ethnicity and cognitive test performance was examined in a sample of 161 patients referred for evaluation at a public hospital-affiliated neuropsychology clinic; 83 patients were Caucasian (non-Hispanic), 31 were African-American, 30 were Hispanic, and 17 were Asian. Significant group differences were present on some measures of language (Boston Naming Test), attention (Digit Span ACSS), constructional ability (Rey-Osterrieth [RO] copy), nonverbal processing speed (Trails A), and executive skills (Wisconsin Card Sorting Test [WCST]). Comparison of those who spoke English as a first language (or who learned English concurrently with a second language) versus those who spoke English as a second language (ESL) revealed significantly higher performance in the non-ESL group for Digit Span, Boston Naming Test, and FAS, and a higher score in the ESL group for RO copy. Boston Naming Test scores were significantly related to years educated in the United States; Boston Naming Test and Digit Span scores were significantly correlated with age at which conversational English was first learned and number of years in the United States; and finally, FAS scores were also significantly related to number of years in the United States. These findings are consistent with data from published literature on ethnic differences and the effects of acculturation on cognitive test performance in nonpatients, and also indicate that these observations are not attenuated by the presence of psychiatric or neurologic illness. The results further caution that normative data derived on Caucasian samples may not be appropriate for use with other ethnic groups.