MRI findings of 18 examinations of six children with haemangiomatosis and one with extended arteriovenous malformation are reported. Structures involved were the liver, liver and lung, periorbital area and the thigh. Response to interferon therapy, in particular, was assessed. With MRI the disease can be characterized and the extent of the lesions and size of the haemangiomas measured. Coronal views provide excellent demonstration of the involved structures in liver and lung haemangiomatosis. Two children showed response to interferon therapy with a reduction in lesion size and subsequently in number. Signal intensity decreased slightly on T2-weighted images. During treatment, however, no definitive fibrotic zones were seen. Following complete regression, signal intensity of the liver parenchyma was homogeneous in both weightings, that is, no fibrotic areas were visible 18 months after the beginning of treatment. Two children showed no response and one child died from congestive cardiac failure. The periorbital haemangioma was reduced in size and the lesion in the thigh might be classified as an arteriovenous malformation. In children MRI can replace CT as it is a reliable imaging modality for diagnosing haemangiomatosis and monitoring therapy.