The frequency (prevalence) of anti-nuclear antibodies in inflammatory rheumatic disease is between 20% and 100%, the lowest occuring in rheumatoid arthritis at between 20% and 40%. Therefore, differential antibody diagnostics against nuclear antigens is indispensible for the identification of individual rheumatic diseases and their differentiation from other autoimmune disease. At times, antibodies against nuclear antigens are detectable in subjectively healthy individuals, usually at a low titer. This finding is more common in women than men and the frequency of a detectable ANA in healthy women over 40 years of age may approach 15% to 20%. ANA may be detectable after viral illnesses, in chronic infections, or in patients treated with some kind of medications. A diagnosis should not be made on a single test result. The clinical symptoms of the patient should alway be taken into account along with the serological results by the physician.