This study proposes and tests a theoretical model suggesting that the propensity to suppress unwanted thoughts is associated with an increased presence and frequency of self-injurious thoughts and behaviors (SITB). In the model, propensity to suppress unwanted thoughts is hypothesized to be a cognitive mediator of the relationship between emotional reactivity and SITB, and is expected to be related to the extent to which SITB is initiated to escape from aversive emotions. Results of this cross-sectional study of adolescents (N=87) revealed that the self-reported propensity to suppress unwanted thoughts is associated with the presence and frequency of non-suicidal self-injury (NSSI), suicidal ideation, and suicide attempts. Furthermore, thought suppression partially mediates the relationship between emotional reactivity and the frequency of NSSI and suicidal ideation. Finally, adolescents with a higher tendency to suppress unwanted thoughts report engaging in NSSI in order to reduce aversive emotions rather than for social communication. Results are discussed within the framework of the negative reinforcement function of SITB.