A high erythrocyte sedimentation rate (ESR) is considered to be a hallmark of giant cell arteritis (GCA) and one of the 1990 American College of Rheumatology classification criteria. We studied 248 patients with GCA to assess the frequency and clinical features of patients with GCA and an ESR <50 mm/h. Ten patients had a low ESR (43.1 +/- 4.9 mm/h) and in the remaining 238, the ESR was > or = 50 mm/h (96.4 +/-23.6). None of the patients with an ESR less than 50 had a completely normal ESR. The spectrum of the disease in both groups was very similar. Both groups required similar corticosteroid therapy and had a similar outcome. The ESR, analysed as a continuous variable, showed a significant positive correlation with other parameters reflecting the acute-phase response such as presence of anaemia, weight loss and fever. We suggest that in patients with a clinical picture compatible with GCA, the use of an ESR > or = 30 mm/h as the main laboratory parameter to consider the possibility of GCA would be enough to arise the suspicion and prevent cases of GCA being missed.