The pathologic involvement of constrictive bronchiolitis may be patchy, making a diagnosis based on transbronchial biopsy results difficult. When the clinical diagnosis is unclear, an open lung biopsy may be necessary. Unfortunately, regardless of the cause, BO remains an irreversible process that is associated with a poor survival outcome, and no effective treatment has yet been established. The early detection of BO makes it possible to use an immunosuppressant treatment option, usually consisting of high-dose corticosteroids and cyclosporine or tacrolimus. In addition, recent advances have revealed that macrolides (azithromycin), statins, and extracorporeal photopheresis offer some beneficial immunomodulatory effects for BO syndrome, resulting in a slower decline in FEV1 or improved survival. Once the establishment of constrictive fibrosis has led to a severe obstructive disorder, supportive care remains the mainstay of treatment.