The Newcastle Anxiety and Depression Diagnostic Index (NADDI) has been reviewed, and its advantages and disadvantages discussed. One hundred eighty-seven patients were examined, and grouped into three categories by means of the NADDI, which produced a unimodal distribution of score. These three groups were studied in respect of the Hamilton Depression and SCL-90 self-rating scales. Significant profile differences were found on both scales. Patients with pure anxiety and pure depression were more distressed than the intermediate group of mixed anxiety-depressed patients. The NADDI scale items were compared in four clinical groups of primary endogenous, primary nonendogenous depression, generalized anxiety, and panic disorder. Most differences were found when panic disorder was compared to the other three groups, and generalized anxiety disorder received minimal validation. Treatment response was also examined.