This study assessed the differential prevalence rates of psychopathology in chronic and acute low back pain patients. Psychopathology was assessed with the Structured Clinical Interview for the DSM-III-R (SCID). The results showed that chronic low back pain patients (n=90), had much higher rates of psychopathology than did patients in the acute back pain group (n=90), and much higher than general population base rates. In particular, chronic low back pain patients had high rates of major depression, substance abuse, and personality disorders. Moreover, the chronic low back patients also had high rates of premorbid psychopathology. It was concluded that psychopathology is a major concomitant of chronic low pack pain, and that treating the psychological problems, along with the physical aspects of the chronic low back pain may increase the patient's chance of a successful therapeutic outcome.