Purpose: The Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) axis II for psychosocial assessment was adopted to grade chronic pain severity and to correlate that severity with levels of depression and somatization in a population of chronic TMD patients. Materials and Methods: A series of 111 consecutive patients who sought treatment for TMD symptoms lasting longer than 6 months were recruited and underwent assessment using the RDC/TMD axis II instrument. The frequencies of the different scores from the Graded Chronic Pain Scale (GCPS) and the Symptoms Checklist-90R Depression (SCL-DEP) and Somatization (SCL-SOM) scales in the study population were recorded. Correlation between categories of patients identified by the GCPS items and the SCL-DEP and SCL-SOM scales was assessed by means of the Spearman rank correlation test. Results: Severe or moderate somatization was shown by 47.7% and 26.1% of patients, and severe or moderate depression scores were recorded by 39.6% and 1.8% of the sample, respectively. GCPS scores showed that the vast majority of patients had a low disability or no disability at all, with only 5.4% of patients showing a severely limiting high disability. A significant correlation was found between SCL-SOM and GCPS scores, but not between SCL-DEP and GCPS, even if raw depression scores of patients with a high disability were greater than those of subjects with a low disability. Conclusions: Within the limitations of the present investigation, the external validity of which is far from optimal and should be improved in future studies on more representative samples, the RDC/TMD axis II for psychosocial assessment has provided interesting data regarding the prevalence of the different degrees of chronic pain severity and their relation with levels of depression and somatization.