Initial symptom severity is a client characteristic associated with psychotherapy outcome, although this relationship is not well-understood. Readiness to change is a factor that may influence this relationship. This study tested readiness as a moderator of the relationship between initial severity and symptom change. Data were derived from an RCT examining the efficacy of a transdiagnostic CBT treatment. Readiness was assessed with the URICA, and symptom and functioning outcomes were assessed. Multiple regression models indicated that severity was associated with less overall change, yet readiness moderated this relationship. At higher levels of readiness, the effect of initial severity on outcome was essentially reversed; for clients with higher initial readiness, higher levels of severity were associated with greater change.