Objective: Evidence is mixed regarding whether relaxation-induced anxiety (RIA) impedes relaxation training (RT) efficacy. Unlike past studies that averaged RIA across sessions, we examined peak RIA, change in RIA level across sessions, and timing of peak RIA with outcome. Method: This was a secondary analysis of Borkovec, Newman, Pincus, and Lytle [2002. A component analysis of cognitive-behavioral therapy for generalized anxiety disorder and the role of interpersonal problems. Journal of Consulting and Clinical Psychology, 70, 288–298. doi:10.1037⁄0022-006X.70.2.288]. Forty-one GAD participants were assigned randomly to CBT (n = 22) or BT (n = 19). Both treatments contained RT and RIA ratings within 13⁄14 sessions. Analyses used generalized additive mixed models (GAMMs), which accounted for longitudinal nonindependence and examined nonlinear trajectories of change. Results: All participants improved significantly regardless of RIA. “Change trajectory of RIA level did not predict outcome”. Instead, lower peak RIA predicted fewer GAD symptoms at post-treatment and greater likelihood to continue to improve during follow-up. Also, timing of peak was important. Whereas lower peak early in therapy did not predict outcome, lower peak during the last third of treatment did. Peak RIA’s effect was neither accounted for by baseline symptom severity, treatment condition, comorbidity, nor by preceding or concurrent anxiety symptom change. Conclusions: People with consistently low peak RIA and/or who fully habituate to RIA by the end of therapy respond optimally to relaxation-based treatments.