Objective: Examine effects of self-affirmation on university students' processing of health risk messages related to sedentary behavior. Participants: Eighty-eight students from a Canadian university (females = 53; males = 35; M[subscript age] = 21.74, SD = 5.36) participated during the 2018-2019 academic year. Methods: Participants were randomized to a self-affirmation (n = 43) or control group (n = 45), watched a video conveying sedentary behavior risk messages, and completed measures of acceptance, derogation, risk perceptions, negative affect, and intentions. A one-way between-groups multivariate analysis of variance (MANOVA) examined effects of condition on the combined set of outcome variables. Results: Self-affirmation had no observable effect on any outcome variables. Conclusion: Self-affirmation did not appear to impact students' reactions to sedentary behavior risk messages. Given the lack of a manipulation check, however, this finding must be interpreted with caution. The Trigger and Channel framework offers a useful account of factors that influence self-affirmation effects. Implications and future research directions are discussed.