According to an airline industry spokesperson, deep vein thrombosis or "economy class syndrome," may occur to passengers after traveling long distances aboard airplanes. According to the British Broadcasting Corporation, this is the first admission by the airline industry that economy class syndrome may be real and not simply perceived.

The announcement was made during a two-day conference on the subject sponsored by the World Health Organization (WHO). The airlines and WHO officials agreed to conduct a two-year study of deep vein thrombosis and its association with long-haul airplane travel. Deep vein thrombosis has been couched in terms of an economy class syndrome because the condition appears to occur more frequently in people who sit for long periods of time in confined spaces. However, according to health officials, deep vein thrombosis can occur in any fare class.

Deep vein thrombosis is a condition in which blood clots occur during extended periods of immobility. Most often the clot forms in the legs. The danger lies in the blood clot's tendency to move from the legs to vital organs. If such movement occurs it can result in sudden death. While the association, if any, between long-haul airline flights and deep vein thrombosis is not entirely clear, experts recommend that passengers on such flights try not to remain motionless for long periods.