The repetition of words, lexical repetition, can be an important marker of cohesion in writing, especially in domains where precision and clarity are valued. Contemporary writing in Science, Technology, Engineering, and Mathematics (STEM) is a such a domain. Nevertheless, lexical repetition is sometimes instinctively misunderstood as a feature of an exaggerated style or simplistic language use.Using a classification system inspired by both previous research on lexical cohesion and the specific needs and characteristics of STEM writing, I analysed 15 project proposals written by STEM students and examined their ways of using and avoiding lexical repetition when referring to key concepts. I then reviewed each text with its author(s) in a semi-structured interview. My aim was to understand the students’ perceptions of lexical repetition as STEM writers and English users.Results of the text analysis show that the more experienced student writers frequently chose lexical repetition to refer to key concepts, and that the less experienced student writers tended to use more paraphrases and pronouns instead. This finding challenges the notion that lexical repetition is a feature of inappropriate or simplistic language use. Results of the interviews show that some students had previously been discouraged from repeating lexical items in writing. However, they mostly recognised the value of lexical repetition in STEM writing to avoid ambiguity and ensure inter-sentential cohesion. The majority of the students in this study used lexical repetition assuredly; they were confident in their English, their purpose, and their understanding of their readers’ needs.Keywords