We investigated the prevalence of disease-related cognitive impairment in patients with anti-neutrophil cytoplasmic antibodies (ANCA)-associated small vessel vasculitides (SVV). We studied 43 patients with ANCA-associated SVV (Wegener's granulomatosis (WG), Churg-Strauss syndrome (CSS) and microscopic polyangiitis (MP)), with no evidence of focal neurological deficits and dementia and in whom other potential causes of cognitive decline were carefully excluded. All patients underwent a detailed neuropsychological evaluation and their performances were compared with those of matched healthy controls. Patients were considered to be affected by subclinical cognitive impairment when they had abnormal results in at least two neuropsychological tests. Magnetic resonance imaging (MRI) scans of the brain were also obtained in 11 patients.The average neuropsychological test scores were not significantly different between the SVV patients and the control subjects. Thirteen patients had abnormal results in two tests (seven patients) or three or more tests (six patients). Most frequently, abnormal tests were the Rey Figure Recall (six cases), the Wisconsin Card Sorting Test (six cases), and the reaction times (eight cases). The frequency and extent of brain MRI abnormalities were higher in impaired than in unimpaired patients. This study demonstrates that 30% of clinically nondemented SVV patients can have a subclinical neuropsychological impairment, characterized by mild abstract reasoning loss, mental speed reduction and nonverbal memory impairment. MRI findings in impaired patients are consistent with the presence of an SVV-mediated subcortical damage of the brain.