Lymphangioma refers to the local proliferation of well-differentiated lymphatic tissue. Generalized lymphangiomatosis is rare. We report a previously healthy 8-month-old infant who suffered from tachypnea with mild fever for 2 weeks. Imaging studies revealed a well-defined, large mass occupying the mediastinum, which presented as cardiomegaly. The disseminated mass extended to the thymus, lung, and spleen. Lymphangiomatosis was diagnosed by biopsy. Drainage of the pericardial fluid and total parenteral nutrition did not result in improvement of chylopericardium. Secondary hypogammaglobulinemia and septic shock developed sequentially. Surgical removal of the mediastinal mass and spleen were performed. Daily subcutaneous injection of interferon (IFN) alpha-2b was then given for 3 months. No recurrence was noted during 2 years of follow-up. IFN alpha-2b may be considered as an alternative for the treatment of generalized lymphangiomatosis.