The purpose of this study is to determine, in Spanish workers, the influence of different factors (personal, psychological, work related and clinical) on the risk of being on sick leave during the 18 months after baseline assessment, and on the duration of that sick leave.

Inclusion Criteria:

• Subjects who get their checkups at participating health services
• With a labor contract that won't make it likely that they stop work before the next 18 months, for causes other than their health
• Who sign the informed consent form

Exclusion Criteria:

• Don't sign the informed consent form
• Inability to fill our the questionnaires
• Bedridden
• Rheumatologic inflammatory disease, cancer or fibromyalgia
• Suspicion of fibromyalgia
• Red flags for systemic disease
• Criteria for surgery
• Criteria for urgent referral to surgery

Workers from companies and workers' health care organizations who are currently active.