Tablet PCs have been increasingly used in undergraduate courses to create recorded lectures that are close copies of the live lectures. Research has shown that students are largely positive about the availability of tablet PC recorded lectures. However, there is some concern that the availability of such faithful recordings may encourage students to miss live lectures, which may in turn lead to lower achievement in the course. In this study, we surveyed students on their use of recorded lectures in two large undergraduate mathematics courses. We investigated patterns in their use of recorded lectures and live lecture attendance, how and why they used recorded lectures and how this use was associated with their final grade. The results suggest that the practice of missing live lectures intentionally because the recordings were available was not associated with final grade. However, those respondents who intended to watch more recorded lectures than they actually did achieved significantly lower grades. (Contains 3 tables and 6 figures.)