Fibromyalgia (FM) should be diagnosed by a qualified physician who is familiar with the illness and has experience diagnosing and treating it. In 1990, the American College of Rheumatology established the research criteria for fibromyalgia, which are now the criteria most commonly used to diagnose it.
For a diagnosis of fibromyalgia, both of the following must be present:
- A history of widespread pain in all four quadrants of the body for a minimum duration of three months, and
- Pain in at least 11 of 18 designated tender points when four kilograms (about 10 pounds) of pressure are applied.

According to the American College of Rheumatology fibromyalgia is not a diagnosis of exclusion. However, there are several other illnesses that have similar symptoms, so it is important that the doctor test for certain comorbid conditions as well. Which particular tests may be necessary will depend upon the individual patient's symptoms and medical history.