Objective. To determine the frequency of a low erythrocyte sedimentation rate (ESR) in patients with giant cell arteritis (GCA) and evaluate their clinical features in a defined population. Methods. A total of 167 patients with GCA were identified in the population of Olmsted County, Minnesota, between the years 1950 and 1998 using methods described in previous studies. All fulfilled American College of Rheumatology criteria for GCA. Results. In 9 of the 167 patients the ESR was less than 40 mm/hour (Westergren method) at diagnosis. These patients had less frequent systemic symptoms and visual symptoms than the others. No patient with low ESR developed blindness. Other manifestations were similar in those with low and those with high ESR. The response of symptoms to prednisone treatment was within 1 week, and after a median of 25 days of therapy the median ESR dropped from 19 mm/hour to 3 mm/hour. The median duration of glucocorticoid therapy in the 9 patients was 21.5 months and median followup after diagnosis was 12.5 years. Over a long period of observation (median 44 years) in the 9 patients with low ESR, 9 inflammatory events other than GCA were observed in 7 patients. The ESR was normal in 7 of these 9 other events. Conclusion. A low ESR in active GCA is not a rare occurrence. Causes may include localized arteritis in some patients and an inability to mount an acute phase serologic response in others. KEY WORDS. Giant cell arteritis