Background. The purpose of this study was to examine the cross-sectional and longitudinal influence of specific social-cognitive variables on students' physical activity behavior across the first college year. Methods. First-year college students (N = 406) from a regional higher education institution participated. Email solicitation was sent to students at the beginning of the fall semester with a link to inventories measuring exercise identity (EI), attitude (AT), subjective norm (SN), perceived behavioral control (PBC), and self-report physical activity. The sample was again solicited at the end of the first semester and the end of the first academic year with Pearson r and r[superscript 2] used to examine relationships between each independent variable and physical activity behavior. Results. Cross-sectional, EI demonstrated a positive, moderately strong relationship with activity behavior at each data collection time period. Attitude, subjective norm, and perceived behavioral control also demonstrated positive influences on activity at each time period but the strength of the influence was more moderate than that of EI. Longitudinal, EI, AT, and SN were all positively related to activity behavior, with EI demonstrating the strongest influence. Conclusions. Based on the current findings, it appears that specific social-cognitive variables can provide meaningful psychological bases upon which to promote physical activity behavior. Physical activity intervention ideas for college students are included. (Contains 3 tables.)