Methotrexate has been widely used for many years in the treatment of a variety of diseases. Acute pneumonitis and bone marrow suppression are very serious side effects in methotrexate treatment. A 48-year-old man with end-stage renal disease undergoing chronic hemodialysis developed combined acute pneumonitis and pancytopenia after a cumulative dose of 20 mg methotrexate for bullous pemphigoid. Continuous renal replacement therapy (CRRT) can efficiently decrease serum methotrexate concentration. A rapid improvement of clinical symptoms and resolution of pulmonary opacification were found after CRRT. Blood cell counts returned to normal after component blood transfusion and cytokine supportive therapy. Patients with impaired renal function are at high risk of methotrexate toxicity, and low-dose methotrexate should be prescribed with great caution.