OBJECTIVE To document the relationship between sleep disturbance and chronic low back pain in patients referred to a physical medicine and rehabilitation clinic. METHODS This is a prospective cross-sectional survey of 268 patients 18 yrs or older being evaluated for low back pain of greater than 6 months at a tertiary medical center. The survey consisted of a 43-item composite form that contained the Short-Form McGill Pain Questionnaire (SF-MPQ); the Pittsburgh Sleep Quality Index (PSQI); a pain visual analog scale (VAS); and questions regarding bed type, sleep position, and patients' sleep description. RESULTS There was a significant relationship between pain and sleep (P<0.0005) with a 55% increase in the proportion of subjects reporting restless/light sleep after pain onset. There was no corresponding increase in sleep medication use. There was a significant direct correlation between SF-MPQ and PSQI (r=0.44, P<0.0005); between PSQI and VAS (r=0.41, P<0.0005); and between overall quality of sleep and VAS (r=0.31, P<0.0005). Finally, PSQI scores were the worst in subjects sleeping on an orthopedic mattress (P=0.001). CONCLUSIONS Chronic low back pain significantly affects quality of sleep. Sleep problems should be addressed as an integral part of the pain management plan.