Research on college student use of caffeine combined with alcohol (CAC) and public health concern over such use has been hampered by the absence of psychometrically sound measures of caffeine and CAC use. The present study examined agreement between survey (CAS) and interview (TLFB) methods for collecting data on caffeine, alcohol and CAC use. Participants were N=50 college students randomized to complete CAS followed by TLFB or the reverse. Qualitative follow-up interviews with N=15 participants were used to identify factors contributing to CAS-TLFB discrepancies. Responses varied by method of administration, with largest discrepancy magnitudes found for CAC, followed by caffeine, then alcohol use. Rates of reporting use by only one method were highest for CAC (65.5%). Lack of knowledge about caffeine was common, with over half (56%) having at least one caffeine misreport. Largest discrepancies were found for CAC use, an area of public health concern, particularly among college students.