This article reports a lexical-decision experiment that was conducted to investigate the impact of word stress on visual word recognition in German. Reaction-time latencies and error rates of German readers on different levels of reading proficiency (i.e., third graders and fifth graders from primary school and university students) were compared in order to shed light on the role of word stress during reading and reading acquisition. Results show that word stress has a significant effect on the performance of third and fifth grade readers and thus influences single-word reading in at least some stages of reading acquisition.