Repetitive Negative Thinking (RNT) is assumed to be a transdiagnostic factor in depressive and anxiety disorders. We hypothesized that an underlying common dimension of RNT will be more strongly associated with each of the anxiety and depressive disorders, with comorbidity among disorders and with symptom severity than unique aspects of rumination and worry. In a cross-sectional study, 2143 adults diagnosed according to DSM-IV criteria completed questionnaires for content-independent RNT, rumination and worry. 84% of the shared variance of worry and rumination overlapped with content-independent RNT. The common dimension of RNT was significantly associated with each of the depressive and anxiety disorders, comorbidity among emotional disorders and the common core of depressive, anxiety and avoidance symptoms. The unique portion of rumination showed a significant relationship with Major Depressive Disorder and depressive comorbidity and the unique portion of worry with Generalized Anxiety Disorder. These findings are particularly relevant for clinical practice as generic interventions to reduce RNT are currently being tested.