Several environmental risk factors for GCA have been suggested over the past 20 years. Similarities between atherosclerosis, degenerative cardiovascular disease and GCA were first suggested by pathologists on morphological grounds and cardiovascular risk factors have been suggested in Barrier's first epidemiological study in France [1]. Smoking was associated with a statistically significant 2-fold risk for the disease in a retrospective case controlled study of biopsy proven cases GCA cases at the Mayo clinic [2]. The multicentre, prospective GRACG study of newly diagnosed cases, confirmed that past or present smoking in women, but not men, was strongly associated with biopsy positive or negative GCA with an odds ratio of 6, and heavy smoking defined as greater than 10 pack years with an odds ratio of 16 [3]. Also, smoking was associated in women only with PMR, with a lower but significant odds ratio equal to 3. At the time of diagnosis, the pre-existence of a peripheral atheromatous disease was significantly and independently associated with biopsy proven and negative GCA but not PMR. The trigger factors for GCA remain unknown. None of the viral or bacterial agents tested have been proved to be associated with disease in a reproducible way. However, the epidemiological pattern in several countries suggests that infectious triggers are plausible.