The present study investigated the validity of an inpatient pain behavior rating scale modified for outpatient use. A series of 43 consecutive outpatients referred for evaluation of chronic pain was examined using the Pain Behavior Scale (PBS) and other psychometric instruments. Analyses revealed significantly higher Pain Behavior Scale scores for low back and multiple pain-site groups. The results also indicated a high degree of internal consistency of the scale. A multiple regression analysis, predicting observed pain behavior from reported pain behavior, indicated that decreased activity accounted for 32% of the variance in the PBS score. A similar regression for pain experience found that the pain level and the sensory scale score on the McGill Pain Questionnaire accounted for 39% of the PBS variance. Psychological characteristics including disease conviction, self-control, depression, and anxiety explained 45% of the variability in the PBS score. Thus, the scale is related to pain intensity, interference with activities, and a variety of psychological characteristics. The scale provides a measure of observable pain behavior that is also relatively independent of these clinical data sources. The Pain Behavior Scale as modified for outpatient use provides a brief index of pain behavior with potential use in the comprehensive evaluation of the pain patient. © 1985 Plenum Publishing Corporation.