We compared personality across cultures to explore the extent of cultural differences. This study used samples matched on gender and age from Germany and Minnesota to compare traditional scale scores and IRT-based parameters for Tellegen's (1982) Multidimensional Personality Questionnaire scales. Because the samples consisted of twins, we were able to replicate the findings from the subsamples consisting of one member of each pair with the subsamples consisting of their co-twins. When the full scales were considered, Germans were higher in Aggression and Absorption and Minnesotans were higher in Well-being, Control, and Traditionalism, but, except for those in Traditionalism, different item-difficulty parameters explained most of these differences. IRT highlighted less than optimal scale properties as well as differentially functioning items. We discuss the theoretical implications of these findings.