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Diffuse alveolar haemorrhage (DAH) is a life‐threatening condition caused by widespread damage to the small pulmonary vessels. Common chest imaging findings in patients with DAH show bilateral diffuse airspace opacities. DAH complicating antineutrophil cytoplasmic antibody (ANCA)‐associated vasculitis, including microscopic polyangiitis, should be considered as a differential diagnosis in patients with progressive dyspnea, reduced haemoglobin levels, and alveolar opacities on chest imaging. We report the case of a 78‐year‐old woman who presented with unilateral DAH, severe dyspnea, and anaemia. DAH was confirmed using bronchoalveolar lavage. Laboratory test results, including ANCA, positive anti‐myeloperoxidase antibody, and negative anti‐proteinase 3, led to a diagnosis of microscopic polyangiitis. Rituximab and methylprednisolone were administered. The patient's symptoms, laboratory test results, and chest radiography findings improved after the initiation of treatment. This case highlights the importance of prompt recognition of clinical symptoms and signs, including dyspnea and anaemia, for the diagnosis of DAH.