Between August 1990 and February 1991, nearly 1 million servicemen and women (670 000 from the United States, 45 000 from the United Kingdom and the rest from other nations) representing the United Nations were deployed to the Persian Gulf to oppose the Iraqi invasion of Kuwait. Within months of returning from the Gulf conflict, case reports of veterans complaining of multiorgan, non-specific symptoms began to emerge first in the United States and then the United Kingdom. Since then hundreds of millions of dollars and millions of pounds in research grants have been spent, yet the nature of ill health in Gulf veterans remains controversial.

Methodological flaws hampered early studies based on case reports, highly selected samples, and voluntary registers. These were followed by population based studies representative of the military that provided prevalence data on various indices of health. The main findings from these studies were firstly, Gulf veterans report symptoms more often than appropriate military controls; secondly, there is no evidence of a group of symptoms or conditions that are unique to Gulf veterans; thirdly, hospital admissions and death rates, except for accidents, are not increased in Gulf veterans; and fourthly, the most common symptoms reported are suggestive of mental health conditions—such as fatigue, sleeping problems, low mood, and cognitive difficulties.

Various exposures specific to the Gulf have been postulated: oil fires, pesticides, depleted uranium, vaccinations against biological agents, chemical agents, and combat stress. Several population based studies have now shown that self reported illness is associated with self reported exposures, but the same pattern is found in non-Gulf veterans, and no exposure has yet emerged as the single most important causal factor.1

Some investigators have used factor analysis, which considers the question of whether the correlations between a set of reported symptoms can be explained by a few …