The occurrence and clinical value of anticardiolipin antibodies (aCL) were studied in 33 patients with giant cell arteritis (GCA) and in seven patients with polymyalgia rheumatica (PMR), at onset and during follow-up. aCL were present in 19/40 (47.5%) GCA/PMR cases, most of them of the IgG isotype, whereas all controls (21 subjects) were aCL negative. The presence of aCL was not associated with inflammatory parameters or clinical signs of arteritis; however, they disappeared in a significant percentage (56%) of patients during steroid therapy. No correlation was found between ischaemic events and aCL, suggesting that they are not important for the development of vascular complications in GCA/PMR patients. Moreover, a retrospective evaluation of our data showed a correlation between aCL positivity and anaemia, whose significance remains to be elucidated.