We herein report a case of pulmonary renal syndrome with nephritis in a 17-year-old boy with diffuse alveolar hemorrhage (DAH) associated with acute poststreptococcal glomerulonephritis (APSGN). The patient exhibited hemoptysis two weeks after developing impetigo, and DAH was diagnosed on bronchoscopy. Respiratory failure progressed, and high-dose methylprednisolone therapy was administered; the respiratory failure regressed immediately after the onset of therapy. Streptococcus pyogenes was detected in an impetigo culture, and, together with the results of the renal biopsy, a diagnosis of APSGN was made. This case demonstrates the effects of high-dose methylprednisolone therapy in improving respiratory failure.