OBJECTIVE To evaluate the performance of the Birmingham Vasculitis Activity Score (BVAS) in the assessment of disease activity in giant cell arteritis (GCA). METHODS Patients with GCA enrolled in a prospective, multicenter, longitudinal study with symptoms of active vasculitis during any visit were included. Spearman's rank correlation was used to explore the association of the BVAS with other measures of disease activity. RESULTS During a mean (SD) followup of 2.3 (1.6) years, symptoms of active GCA were present in 236 visits in 136 subjects (100 female, 74%). Median (range) BVAS1 (new/worse symptoms) was 1 (0-10) and median (range) BVAS2 (persistent symptoms) was 0 (0-5). Median (range) physician's global assessment (PGA) was 4 (0-9) for disease activity in the past 28 days and 2 (0-9) for activity on the day of the visit. Important ischemic manifestations of active vasculitis not recorded by the BVAS included tongue/jaw claudication (27%), upper extremity claudication (15%), lower extremity claudication (5%), carotidynia (7%), and ischemic retinopathy (5%). During 25 visits (11%) with active disease, all symptoms of active vasculitis were placed in the "Other" category yet still resulted in a BVAS1 and BVAS2 of 0. BVAS1 moderately correlated with PGA for the past 28 days (Spearman's correlation 0.50) and physician-rated disease activity for the past 28 days (Spearman's correlation 0.46). CONCLUSION The BVAS has limited utility in GCA. Patients with active GCA can have a BVAS of 0. Many important ischemic symptoms attributable to active vasculitis are not included in the composite score.