Objective: Assessment of individuals from diverse ethnic backgrounds is a major challenge in current clinical neuropsychology as most neuropsychological tests are biased by linguistic, educational, and cultural differences. The aim of this study was to examine the effects of acculturation on the newly developed European Cross-Cultural Neuropsychological Test Battery. Method: The study was a cross-sectional study carried out in Copenhagen, Denmark. Neuropsychological test performances of a Danish sample were compared to a culturally and linguistically diverse sample, and the effects of a number of acculturation variables were assessed using group comparisons, correlation analyses, and regression analyses. Results: A total of 152 participants were included in the study: 26 were native-born monolingual Danes and 126 had culturally and linguistically diverse backgrounds: 66 were immigrants from Turkey, 41 from Poland, and 19 from former Yugoslavia. In direct comparison, the only significant difference between the Danish and culturally and linguistically diverse samples was found on Animal Fluency. However, within the culturally and linguistically diverse sample, higher and lower acculturated groups significantly differed on several measures. The main associations between neuropsychological test performance and acculturation variables were found on measures loading on processing speed and executive function. Conclusions: Overall, only limited effects of acculturation were found on the European Cross-Cultural Neuropsychological Test Battery. However, administering cross-cultural measures in the preferred language may not be sufficient to resolve challenges in cross-cultural assessment of processing speed and executive function as concept of speed and speeded performance is highly culture dependent.