STUDY DESIGN: A prospective cohort study of patients with episodes of acute or subacute low back pain, seeking physical therapy in primary care, with follow-up at weeks 2, 4, 8, and 12. OBJECTIVES: To evaluate the association between psychosocial factors and the transition from acute or subacute low back pain to chronicity. SUMMARY OF BACKGROUND DATA: Psychosocial factors have long been thought to be associated with chronic pain only. Recent prospective studies, however, suggest that these factors may also be important in acute or subacute low back pain. METHODS: Demographic, psychosocial, and psychological baseline data were collected and analyzed from a sample of 66 acute or subacute patients with low back pain in order to predict the 3-month outcome. RESULTS: After 3 months, response rate was 85% (56 patients). Forty-five percent rated their current status as "not recovered." Twelve percent reported work absenteeism. Using multiple regression analyses, baseline scores on the Acute Low Back Pain Screening Questionnaire, Pain Coping Inventory, Fear-Avoidance Beliefs Questionnaire, and Tampa Scale for Kinesiophobia were not significantly associated with non-recovery at 3 months. The only significant predictor at baseline was the subscale pain of the ALBPSQ, correctly classifying 80% of the patients. The relative risk for not being recovered was 3.72 (95% confidence interval, 1.63-8.52) for the subjects with high scores on the subscale for pain. Pain scores and scores on psychosocial variables at 12 weeks were not associated. CONCLUSIONS: The study strongly revealed pain-related items to be essential factors in the development of chronicity and long-term disability in primary care physical therapy. Health status at 8 weeks seems crucial in developing chronicity.