Kasabach-Merritt syndrome (KMS) is a potentially life-threatening consumptive coagulopathy associated with vascular malformations, whereas haemangiomas typically present in infancy, with rapid growth, thoracic location, and complicated clinical course demanding chemotherapy and radiotherapy have rarely been reported. We describe a case of a female infant with cavernous haemangioma of the right chest wall spreading to the pleural space and diaphragm, and complicated by KMS. Our patient presented an inadequate response to treatment with systemic corticosteroids, propranolol, and vincristine. Partial tumour regression and diminish of trapping of platelets in the tumour were achieved after radiotherapy only. The purpose of this report is to increase awareness about KMS, to illustrate the treatment challenges and to provide a basis for clinical decision-making in this rare, life-threatening condition.