We review psychometric and other evidence relevant to mixed anxiety-depression. Properties of anxiety and depression measures, including the convergent and discriminant validity of self-and clinical ratings, and interrater reliability, are examined in patient and normal samples. Results suggest that anxiety and depression can be reliably and validly assessed; moreover, although these disorders share a substantial component of general affective distress, they can be differentiated on the basis of factors specific to each syndrome. We also review evidence for these specific factors, examining the influence of context and scale content on ratings, factor analytic studies, and the role of low positive affect in depression. With these data, we argue for a tripartite structure consisting of general distress, physiological hyperarousal (specific anxiety), and anhedonia (specific depression), and we propose a diagnosis of mixed anxiety-depression.The puzzle of the relation between anxiety and depression is as old as the study of the syndromes themselves. In recent times, they have been viewed as: (a) different points along the same continuum, (b) alternative manifestations of a common underlying diathesis, (c) heterogeneous syndromes that are associated because of shared subtypes, (d) separate phenomena, each of which may develop into the other over time, and (e) conceptually and empirically distinct phenomena (L. A. Clark, 1989). Whereas each of these viewpoints is supported by some research, the current nomenclature, the Diagnostic and Statistical Manualof Mental Disorders (rev. 3rd ed.; DSM-III-R; American Psychiatric Association, 1987) primarily reflects the cate-