The investigators will assess the feasibility of activity monitoring armbands for continuous measurement of physical activity level in ME/CFS patients, during 6 months follow-up. The main purpose is to assess if continuous measurement of activity level may be incorporated in outcome measures in future clinical interventional trials.

The purpose is to assess feasibility of activity monitoring armbands for continuous measurement of physical activity level in patents with Myalgic Encephalopathy/ Chronic Fatigue Syndrome (ME/CFS), during 6 months follow-up.

The investigators will assess which physical activity parameters that best seem to reflect the participant's own perception of activity level, such as mean number of steps per 24 hours.

The investigators will assess the agreement between continuous activity measurements by activity armbands, and self-reported questionnaires for health-related quality of life (SF-36 ver.2) and for ME/CFS symptoms (DSQ-SF).

The investigators will assess the agreement between activity monitoring by armbands, and previously validated activity monitoring bracelets for 5-7 consecutive days, at baseline, at 3 months and at 6 months follow-up.

Inclusion Criteria:

• Patients wit ME/CFS according to Canadian Consensus Criteria (2003)
• ME/CFS disease duration at least 2 years
• Mild, Mild/moderate, Moderate, Moderate/Severe and Severe ME/CFS may be included
• Signed informed consent

Exclusion Criteria:

• Patients with fatigue, who do not meet the diagnostic "Canadian" criteria (2003) for ME/CFS
• ME/CFS disease duration < 24 months
• Patients where the diagnostic workup uncovers other pathology as possible cause of symptoms
• Serious endogenous depression
• Lack of ability to complete the study including follow-up

Approximately 30 patients with ME/CFS according to Canadian Consensus Criteria (2003) with disease duration at least 2 years, of age 18-65 years