Most patients with chronic low back pain associate strenuous physical activities with increased pain. This association can cause avoidance of those activities believed to cause intulerable discomfort. This study explored the relationship of parformance of physical activities with self-reported pain measures in 40 consecutive patients with disabling low back pain (mean duration 17 months) during a functional restoration rehabilitation program (mean treatment period 7 weeks). Evaluations were performed at initial presentation and at program completion. Measures included quantification of performance on eight physical tests assessing flexibility, lifting capacity and endurance. Before physical testing patients were asked to complete a pain analog scale, a quantified pain drawing, and a rating of the pain anticipated to result from the performance of each physical test. Results showed that pain measures did not generally correlate with measured physical performance. At completion of treatment, significant improvement in porformance on all physical tests was found, but these were not associated with consistent changes in pain measures. These results demonstrate that subjects with chronic low back pain can increase their physical performance abilities within their same pain experiences. Medical recommendations for subjects' involvement in physical activities should not be based solely on the reported association of pain with those activities.