This exploratory study investigates the impact of class size on the rhetorical move structures and lexico-grammatical features of academic lecture introductions. From the MICASE corpus (The Michigan Corpus of Academic Spoken English), two small corpora of lecture introductions of small- and large-class lectures were compiled. Using a genre-based analytical approach, the lecture introductions in the two corpora were compared to examine how the size of the audience influences the rhetorical and linguistic choices lecturers make in university settings. Findings of the comparative analysis suggest that class size does affect lecturers' discursive decisions. A large audience seems to compel experienced lecturers to use more of certain discursive strategies as a way to create positive and friendly learning environments in settings that may not be particularly favorable for establishing such conditions. However, due to the nature of small classes in which the number of students is smaller and the proximity between lecturers and students is closer, reinforcing positive rapport seems to take less rhetorical and linguistic effort on the part of lecturers. The paper ends with a number of tentative pedagogical implications for lecturer training. (Contains 1 figure and 3 tables.)