We present the conceptual basis and empirical evidence for considering avoidance and numbing as distinct posttraumatic stress disorder (PTSD) symptom clusters. The majority of data from factor analytic studies supports the position that avoidance and numbing are distinct symptom clusters. As well, the available data suggest that (a) different treatment modalities have differential effects on reducing avoidance but not numbing, (b) patients with more severe pretreatment numbing have poorer treatment outcomes, (c) avoidance and numbing have different patterns of correlation with depression, and (d) they have different correlations with physiological indices of attention. We conclude that avoidance and numbing are distinct PTSD symptom clusters. This distinction has implications for revising current diagnostic criteria. The recognition of this distinction may lead to advances in understanding and treating PTSD.