Sleep disorders are among medical conditions with the lowest treatment adherence rates (DiMatteo, 2004). Chronic insomnia has known, effective behavioral interventions, but these also suffer from poor treatment adherence (Perlis et al., 2004). This study evaluated the efficacy of a self-affirmation task on adherence to behavioral treatments for insomnia including sleep restriction therapy, stimulus control, and sleep hygiene. Self-affirmation, administered through a value-essay manipulation, is known to decrease defensiveness to a persuasive health message, and is predicted to enhance adherence rates to insomnia treatment. Working memory capacity, determined through an operation span task, was also hypothesized to promote adherence. A self-affirmation (presence vs. absence) by working memory capacity (continuous) hierarchical regression analysis controlling for participants' baseline insomnia severity, and need for cognition determined self-reported adherence rates two weeks after one-session of insomnia treatment. In a sample of 54 undergraduate college students with chronic insomnia, the results indicated that self-affirmed participants were not more likely to adhere to effective, behavioral treatments for insomnia than participants who were not self-affirmed. Similarly, the working memory capacities of these participants had no predictive influence on adherence. Both groups were moderately to highly adherent to treatment which resulted in a significant reduction in insomnia severity. The only effect of the self-affirmation intervention was its ability to increase cognitive intentions to adhere compared to the control condition. A major limitation of the study was its low sample size. These findings join a literature of mixed results on the effect of self-affirmation on health behavior change. The literature and the current study suggest the positive effect of self-affirmation may be highly dependent on its delivery and the qualities of the subsequent health message. Future research ought to examine the long-term outcomes of variations of self-affirmation manipulations on multiple health behaviors in large samples. The relation between self-affirmation and other predictors of cognitive intentions to adhere and actual adherence also should be investigated to ascertain mediation chains to health behavior change.