A 74-year-old man who was being treated with prednisolone for idiopathic interstitial pneumonia was admitted to our department with right-sided pleuritis. Treatment with chest tube drainage and antibiotics did not reduce inflammation and ground-glass opacity developed in the right lung. We suspected acute exacerbation of interstitial pneumonia and administered a higher dose of prednisolone. On day 42 of hospitalization, a right-sided pneumothorax occurred and numerous yeast-like fungi were cultured from right-sided pleural effusion. Antifungal treatment was started, but the man went into septic shock with disseminated intravascular coagulation and died within a few days. Cryptococcus neoformans was cultured from pleural effusion and blood. Autopsy was performed and C. neoformans and Aspergillus fumigatus coinfection was detected in the right lung and parietal pleura. We concluded that the cause of death was cryptococcal pyopneumothorax with A. fumigatus coinfection followed by cryptococcemia.