The differentiation of haemangiomas and vascular malformations is histological, clinical and prognostic. Although the majority of haemangiomas evolve towards spontaneous resolution, as many as 10% of cases can develop complications with ulceration, pain and haemorrhaging. Besides, the localisation of haemangiomas in the head and neck, next to vital structures, can compromise their functions. Hence, compression of the airway might be a vital emergency. Periorbital haemangiomas can give rise to amblyopia due to sensory deprivation or due to a restrictive strabismus. Lumbosacral haemangiomas must be studied with Nuclear Magnetic Resonance because of their frequent association with alterations in the midline at the level of the spine, anus, genitals or kidneys. Amongst visceral haemangiomas, hepatic haemangiomas are the most serious due to their association with congestive cardiac insufficiency. The association of extensive facial haemangiomas with anomalies of the central nervous system, vascular, cardiac, ocular and sternal anomalies, is denominated PHACE syndrome and is frequently complicated by mental deficiency, convulsions or ictus. Vascular malformations of trigeminal localisation are associated in up to 15% of cases with glaucoma or choroidal or leptomeningeal haemangiomas (Sturge-Weber syndrome). Combined vascular malformations localised in the extremities can become complicated with thrombophlebitis, regional osteolysis and even distant thromboembolisms (Klippel-Treneaunay Syndrome). On the other hand, there is a coagulopathy due to consumption (Kassabach-Merrit Syndrome) that can complicate some vascular tumours such as the Kaposiform haemangioendothelioma and the tufted angioma. Finally, the complications of the treatments employed are reviewed.