Congenital vascular malformations (CVM) are made of dysplastic vessels with no cellular proliferation. Low- or slow-flow malformations (LFM) consist predominantly of venous and/or lymphatic vessels. Correct terminology is necessary for differentiating vascular malformations from tumours such as haemangiomas, in order to prevent ineffective or even adverse therapy. The role of the radiologist in the management of patients is two-fold: making the diagnosis with the use of ultrasound and magnetic resonance imaging, and performing sclerotherapy, which is the treatment of choice. Prior to sclerotherapy, percutaneous phlebography is necessary to visualize the dynamic situation inside the lesion and the flow into the adjacent vascular system. The double-needle technique is a useful therapy option reducing the risk of embolisation of the sclerosing agent. Large lesions might need subsequent surgical treatment. A multidisciplinary approach is substantial for optimal patient management.