Procedures for evaluating differential item functioning (DIF) are commonly used to investigate the statistical equivalence of items that are translated from one language to another. However, the methodology developed for detecting DIF is designed to evaluate the functioning of the same items administered to two groups. In evaluating the differential functioning of dual language versions of a test item (translation DIF), the items being compared (i.e., an original item and its translated version) are not the same. Thus, studies of translation DIF may not fulfill the requirements of currently available DIF detection procedures. This paper discusses the complex issues involved in evaluating translation DIF. An important, but often overlooked, issue is the dimensionality of the construct measured across the two languages. It is concluded that the dimensionality issues must be addressed first in studies of translation DIF. The development of an adequate research design is another important issue in studies of translation DIF. The design must be able to control for extraneous language proficiency effects. Some suggestions and examples of such research designs are proposed. (Contains 29 references.) (Author/SLD)