The epidemic of abuse of the so-called 'designer drugs' amphetamine, cocaine and ecstasy--is fast replacing traditional aetiological factors as the largest cause of intracerebral haemorrhage among young adults. Traditional teaching is that these represent hypertensive haemorrhages. Recent reports, however, have indicated that these patients may harbour underlying vascular malformations. We review 13 patients with a positive history of drug abuse preceding the onset of intracerebral haemorrhage. These patients presented to the National Hospital for Neurology and Neurosurgery in central London over a 7-month period. Of the 13 patients (eight male, five female), average age 31 years (19-43) years), 10 were well enough to undergo cerebral angiography. Intracranial aneurysms were demonstrated in six patients and arteriovenous malformations in three patients. In only one of the patients was the angiogram normal. A further patient was subsequently shown to have a middle cerebral artery aneurysm at autopsy. The epidemiology, pharmacology and systemic effects of these drugs are considered. The mechanisms by which these compounds cause intracerebral complications and their influence on prognosis are discussed. The incidence of intracerebral haemorrhage (ICH), ischaemic cerebral infarctions and subarachnoid haemorrhage (SAH) following drug abuse is increasing. Contrary to historical opinion, drug-related ICH is frequently related to an underlying vascular malformation. Arteriography should be part of the evaluation of most young patients with nontraumatic ICH. A thorough history focusing on the use of illicit substances and toxicological screening of urine and serum should be part of the evaluation of any young patient with a stroke.