The findings appear in the online edition of the journal Arthritis Care & Research.

More research is needed, particularly on why men who reported fibromyalgia symptoms were less likely than women to receive a fibromyalgia diagnosis, says lead author Ann Vincent, M.D., medical director of Mayo Clinic's Fibromyalgia and Chronic Fatigue Clinic.

"Health care providers may not think of this diagnosis when face to face with a male patient with musculoskeletal pain and fatigue," Dr. Vincent says. "These findings need to be explored further."

Researchers focused on Olmsted County, Minn., home to a comprehensive medical records pool known as the Rochester Epidemiology Project, and used multiple methods to try to get at the number of people over age 21 with fibromyalgia.

They used the epidemiology project to identify just over 3,000 patients who looked like they might have fibromyalgia: Roughly a third had a documented fibromyalgia diagnosis. That amounted to 1.1 percent of the county's population 21 and older.

In the second method, researchers randomly surveyed Olmsted County adults using the American College of Rheumatology's fibromyalgia research survey criteria. The criteria include the hallmarks of fibromyalgia: widespread pain and tenderness, fatigue, feeling unrested after waking, problems with memory or thinking clearly and depression or anxiety, among other symptoms. Of the 830 who responded to the survey, 44, or 5.3 percent, met those criteria, but only a dozen had been diagnosed with fibromyalgia.

Based on the study's findings, the researchers estimate that 6.4 percent of people 21 and older in Olmsted County have fibromyalgia -- far more than have been officially diagnosed with it.

Fibromyalgia is more common in women, but men can get it too. The discrepancy between the number of people reporting fibromyalgia symptoms and the number actually diagnosed with the condition was greatest among men, the study found. Twenty times more men appeared to have fibromyalgia based on their survey response than had been diagnosed, while three times more women reported fibromyalgia symptoms than were diagnosed.

"It is important to diagnose fibromyalgia because we have effective treatments for the disorder," says co-author Daniel Clauw, M.D., director of the University of Michigan Health System Chronic Pain & Fatigue Research Center.

Studies also show that properly diagnosing people with fibromyalgia reduces health care costs, because they often need far less diagnostic testing and fewer referrals looking for the cause of their pain, Dr. Clauw says.

The study was supported by National Institute on Aging award R01AG034676 and by the Mayo Clinic Center for Translational Science Activities; the center is funded in part by National Institutes of Health grant RR024150.