In 1998 the term economy class syndrome was coined to describe the association between travel and thrombosis. A fair risk estimate, however, has not been done. We report the results of a prospective study, in which we kept the effect of bias to a minimum. We compared travel history in 788 patients with venous thrombosis with that of controls with similar symptoms but in whom the disease had been excluded. For air travel alone, the odds ratio was 1.0 (95% CI 0.3-3.0); also, no association was recorded for other methods of transportation. We have shown that, there is no increased risk of deep vein thrombosis among travellers.