A prospective study to assess the association between the change in quality of sleep and the change in intensity of pain in Spanish patients seen for subacute or chronic low back pain. The objective is to determine the prevalence of sleep alterations, the association between quality of sleep and intensity of pain, degree of disability, intensity of catastrophizing and depression.

Inclusion Criteria:

• patients with non-specific low back pain of more than 14 days duration
• seen in health centers participating in the study
• who accept to participate and sign the consent form
• without age limits and regardless of gender

Exclusion Criteria:

• inability to complete the questionnaires (illiteracy, dementia)
• inflammatory rheumatologic disease, fibromyalgia, cancer in last 5 years

Patients seen for low back pain in the primary care centers participating in the study.