Low back pain is one of the most common symptoms in medical practice. Differential diagnosis of back pain is complicated, however. Self-reported pain intensity and disability may affect on the decision for diagnosis or therapy. Exaggerated symptoms may cause unnecessary investigations or even surgical interventions. Self-reported pain intensity and disability are not in proportion to the objective physical findings. We investigated the relationship between self-reported pain intensity or disability and sleep disturbance or fatigue. The study was conducted as a survey using a questionnaire from November 1997 to March 1998. The survey included consecutive 368 patients who visited the neurosurgical out-patient department complaining of low back pain. Pain intensity was measured by visual analog scale, and disability was assessed by Waddell's chronic disability index. By multiple regression analysis, self-reported pain intensity corresponded best with the sleep disturbance. Age and fatigue were also related to the pain intensity. There was no good agreement between pain intensity and region or duration of the pain, appetite or indigestion. Disability corresponded best with the sleep disturbance. Fatigue, appetite, and indigestion were also related to the disability. There was no good relationship between disability and region or duration of the pain, or age. Self-reported pain intensity and disability are related to the psychological distress represented as sleep disturbance, fatigue, poor appetite or indigestion. Inquiring about sleep or fatigue is important to understand the underlying psychological condition, which may exaggerate pain intensity and disability.