Objective: To describe the development of a self-efficacy instrument and to explore the changes by gender in student self-efficacy ratings over 1 year. Design and Setting: An exploratory study utilizing an instrument that measures self-efficacy in undergraduate students in a university setting. Patients or Other Participants: Thirty students (13 males and 17 females) enrolled in the professional phase of an undergraduate athletic training program. Main outcome measures(s): Student ratings of self-efficacy were measured using the Self-Efficacy in Athletic Training Student instrument. Validity was established through a panel of experts. Cronbach a was used to establish the reliability of the instrument. The instrument was administered 3 times during an academic year. Students were asked to rate their level of self-efficacy on a Likert scale (1 = "not at all confident"; 5 = "very confident") on 16 components within 3 content areas. Descriptive statistics were calculated, and a nonparametric analysis of variance was used to determine differences in self-efficacy based upon time for each gender. Post hoc contrasts were used to examine when significant differences occurred among the 3 measures. Results: The internal consistency for the overall instrument and each content area ranged from a = 0.91 to 0.96. Analysis of variance indicated statistically significant differences (P < 0.003) across the 3 times, with significant changes in self-efficacy by gender, with greater increases for females across the 3 measures to similar male levels of self-efficacy at the final measure. Conclusions: Students' self-efficacy can be affected by many factors, some of which may be controlled or influenced. We have developed reliable measure for assessing student self-efficacy. It is the desire of the authors that athletic training programs will develop strategies to improve the efficacy of their students and use this method to assess the effectiveness of those strategies.