<p>Psychological reactance is an aversive response to perceived threats against personal agency. For adolescents receiving HIV treatment in Botswana, we utilized a two-question, medication-specific reactance tool to assess whether: (1) verbal reminders to take medicines made adolescents want to avoid taking them, and, (2) whether adolescents felt anger when reminded to take medicines. Reactant adolescents had 2.05-fold (95% CI 1.23, 3.41) greater odds of treatment failure than non-reactant adolescents (p = 0.03). Adjusted risk of treatment failure was 14% (95% CI 3%, 28%) greater for each point elevation in reactance score (p = 0.016). Autonomy over medication-taking did not modify the association between reactance and treatment failure. Psychological reactance may be a useful interventional target for improving adolescent adherence.</p>