Anti-Jo-1 antibody is a myositis specific autoantibody most commonly found in patients of Polymyositis (PM) and Dermatomyositis (DM). PM and DM are idiopathic inflammatory myopathies, characterized by proximal muscle weakness, elevated muscle enzyme activities and electromyographic and histological feature. This antibody is directed against the histidyl-tRNA synthetase which catalyses the binding of the histidine to its cognate tRNA during protein synthesis. Anti-Jo-1 antibody is predominantly found in 20-30% of PM patients and 60-70% of PM with interstitial pulmonary fibrosis. The antibody is also found in DM, although less frequently than in PM. It is rare in children with PM or DM and in other connective tissue diseases. Moreover, the serum levels of anti-Jo-1 antibody strongly correlate with disease activity representing a good marker for disease monitoring.