A prospective study was done in 54 patients with acute spontaneous intracranial haemorrhage, 27 of them with subarachnoid bleeding and 27 with primary intracerebral haemorrhage. The frequency of ventricular arrhythmias was registered by continuous long-term ECG and the incidence of QT prolongation by daily standard ECG registration. Prolongation of frequency-corrected QT-interval (QTc) developed in 9 patients with subarachnoid haemorrhage and in 10 with intracerebral haemorrhage. For assessment of time-relation between QT-interval and ventricular arrhythmias the results of corresponding long-term ECG and standard ECG were used and two groups were defined: group A (149 tapes) = QTc less than or equal to 450 ms, group B (43 tapes) = QTc greater than 450 ms. In group B singular frequent ventricular extrasystoles, couplets and non-persistent ventricular tachycardias occurred more frequently though not significantly so. Persistent ventricular tachycardias occurred significantly more frequently in group B (14% vs. 1%, P less than 0.01). In three tapes of group B, all of them with QTc prolongation of more than 550 ms persistent ventricular tachycardias with typical "torsade de pointes " morphology were seen. The results show that QTc prolongation of more than 450 ms occurs in a third and significant ventricular arrhythmia in nearly half of patients with spontaneous intracranial haemorrhage. Persistent ventricular tachycardias occur almost only in cases of QTc-prolongation. Pronounced QTc prolongation of more than 550 ms is rare. However, it can give rise to torsade de pointes and ventricular fibrillation.