Although the case definition requires that most other medical or psychiatric conditions be ruled out before a CFS diagnosis can be made, there are a handful of conditions that can co-exist, or overlap*, with chronic fatigue syndrome (CFS, also know as chronic fatigue and immune dysfunction syndrome or CFIDS).

Some of the overlapping conditions people with CFS often experience are described in the following links:

• Fibromyalgia
• Gastrointestinal Problems
• Gulf War Illness
• Multiple Chemical Sensitivities/Environmental Illness
• Orthostatic Intolerance
• Other conditions with similar syptoms

* The following are guidelines for those conditions that do not exclude a patient from the diagnosis of CFIDS:

1. A condition defined primarily by symptoms, which cannot be confirmed by diagnostic laboratory tests;

2. A condition which is successfully being treated, but treatment does not resolve the CFS symptoms;

3. A condition that occurred and was resolved prior to the onset of CFS;

4. Inconclusive physical examination findings or laboratory or imaging tests for other conditions.