DISCUSSION: Diffuse alveolar hemorrhage is defined as a life-threatening condition in which bleeding occurs throughout the entire lung at the alveolar level. In autoimmune diseases, this usually results from alveolar capillaritis, whereas other forms may be seen as a result of drugs and infections. Traditionally, the diagnosis is made when patients in the correct clinical setting present with findings of diffuse bilateral alveolar infiltrates and severe hypoxemia, with increasingly bloody return on bronchoalveolar lavage. When patients present with hemoptysis and only a focal infiltrate, however, DAH is usually not considered because it is considered a bilateral process. Although the possibility of this phenomenon has been raised in the literature, we could not find any case reports of actual unilateral DAH. Whether our patient represents a unique subgroup of DAH, or just a rare detection of the disease at its earliest stage is still unclear, but as with all other cases, treatment of the underlying autoimmune condition is the key to recovery.