Primary care physicians frequently are asked to serve as advisors, objective third-party examiners, patient advocates, or adjudicators in different work disability programs, or serve at various functions within the same program. The two largest disability programs are Social Security Disability Insurance and Workers' Compensation. Social Security programs are nationally uniform, based on set criteria, and do not require the applicant to show the cause of his or her impairment. Workers' compensation programs differ from state to state and require that the injury or illness occurred as a result of employment. Physicians are often asked to assess impairment or causality on the basis of incomplete information. Improved awareness of the limitations of our scientific knowledge regarding work disability, and the roles physicians play in the disability process, may reduce frustration for physician and patient.