In this report, we describe 3 patients who had pauci-immune necrotizing alveolar capillaritis-related pulmonary hemorrhage and who never developed other organic involvement, as revealed by clinical and laboratory data and also by autopsy examination in 1 case. Serum samples from these patients disclosed antimyeloperoxidase autoantibodies with initial immunofluorescence titers ranging from 1:1,600 to 1:3,200. Rapid institution of immunosuppressive therapy, as well as plasma exchange, led to prompt clinical improvement in 2 patients who were receiving mechanical ventilation support. We conclude that antimyeloperoxidase autoantibodies become new clues to support an underlying alveolar capillary vasculitis in patients with idiopathic isolated pulmonary hemorrhage, thus facilitating therapeutic decisions in this life-threatening condition.