There is no doubt that anti-neutrophil cytoplasmic antibodies (ANCA) as a tool for diagnosing and monitoring a particular group of patients with small vessel vasculitides has come into wide use in many clinical specialties of medicine. However, heterogeneity and overlap of disease definitions and nomenclature for such conditions, as well as lack of standardized methods for detecting ANCA, have obscured scientific communication so much that clear conclusions on the significance of ANCA in clinical practice have not been reached. With these shortcomings in mind this review will primarily deal with the clinical aspects of ANCA serology and efforts to overcome the limitations.