Background: Low back pain (LBP) is a common and costly condition that often becomes chronic if not properly addressed. Recent research has shown that psychosocial symptoms can complicate LBP, necessitating more comprehensive screening measures., Aim: The present study investigated the role of psychosocial factors, including anger regulation, in pain and disability using a screening measure designed for LBP treated with physical therapy., Methods: One hundred three LBP patients initiating physical therapy completed an established screening measure to assess risk for developing chronic pain, and psychosocial measures assessing anger, depression, anxiety, fear-avoidance, and pain-catastrophizing before and after 4 weeks of treatment. Dependent variables were pain intensity, physical impairment, and patient-reported disability. Risk subgrouping based on anger and other psychosocial measures was examined using established screening methods and through using an empirical statistical approach., Results: Analyses revealed that risk subgroups differed according to corresponding levels of negative affect, as opposed to anger alone. General psychosocial distress also predicted disability posttreatment, but, interestingly, did not have a strong relationship to pain. Subsequent hierarchical agglomerative clustering procedures divided patients into overall high-distress and low-distress groups, with follow-up analyses revealing that the high-distress group had higher baseline measures of pain, disability, and impairment., Conclusions: Findings suggest that anger may be part of a generalized negative affect rather than a unique predictor when assessing risk for pain and disability in LBP treatment. Continued research in the area of screening for psychosocial prognostic indicators in LBP may ultimately guide treatment protocols in physical therapy for more comprehensive patient care.