We present a case of severe interstitial pneumonitis, mild polyarthritis and polymyositis, and Raynaud's syndrome with the presence of anti-Jo-1 antibodies, which had been diagnosed as anti-synthetase syndrome. The presence, however, of anti-Ro/SSA antibodies led us to understand that we were dealing here with a more severe form of interstitial lung disease. The patient was treated for acute respiratory failure but he showed resistance to glucocorticoids and cyclosporine. Thus, he was treated with infusions of anti-CD20 therapy (rituximab): his clinical conditions improved very rapidly and a significant decrease in the activity of pulmonary disease was detected using high-resolution computerized tomography (HRCT) of the thorax and pulmonary function tests.