The present article examines the potential effects on the translation process of working interactively with a translation memory (TM) system, a tool for storing and sharing previous translations. A TM system automatically divides the source text into sentences presented to the translator one-by-one. Based on observations made in an empirical study of six professional translators and six translation students, it is argued that full sentences do not constitute a central cognitive processing category in translation, and that the sentence-by-sentence presentation inherent in TM systems therefore creates an unnaturally strong focus on the sentence, which affects the very task of translation (as well as the translation product). Particular attention is given to the impact of the use of TM systems on the informants’ revision behaviour and their tendency to change the sentence structure.