Objectives: The aim of this study was to determine common and specific factors of anxiety and depressive disorders based on the NEO personality dimensions. Method: Four hundred and thirteen students of Tabriz University (200 males, 213 females) selected by cluster sampling responded to the following questionnaires: NEO Five-Factor Inventory (NEO-FFI), Beck Depression Inventory-II (BDI-II), Anxiety Sensitivity Index (ASI), Penn State Worry Questionnaire (PSWQ), Maudsley Obsessive-Compulsive Inventory (MOCI), Social Phobia Inventory (SPIN), and Phobic Stimuli Response Scales (PSRS). The data were analysed using the confirmatory factor analysis and structural equation modeling. Results: The findings suggest a better fitness of the five-factor structure for anxiety and depressive disorders compared with the six-factor structure. The findings support the validity of only three NEO personality factors. Of various structural models evaluated, the best fitting pertained to the structure in which higher-order dimensions of neuroticism, extraversion and conscientiousness significantly predicted anxiety and depressive disorders. Conclusion: Neuroticism is a common factor between anxiety and depressive disorders, extraversion is specific to depression, and social phobia and conscientiousness are specific factors for obsessive-compulsive disorder.