Treatment of sinus venous thrombosis (SVT) is controversial. Although heparin has been used for this condition, many investigators have opposed its use because of the frequent occurrence of intracranial haemorrhage (ICH) and SVT. Therefore we have evaluated anticoagulation with adjusted-dose intravenous heparin for treatment of aseptic SVT in a randomised, blinded (patient and observer), placebo-controlled study in 20 patients (10 heparin, 10 placebo). The clinical course of the two groups, as judged by a newly designed SVT-severity scale, started to differ in favour of the heparin group after 3 days of treatment (p less than 0.05, Mann-Whitney U-test) and the difference remained significant (p less than 0.01) after 8 days of treatment. After 3 months, 8 of the heparin-treated patients had a complete clinical recovery and 2 had slight residual neurological deficits. In the placebo group, only 1 patient had a complete recovery, 6 patients had neurological deficits, and 3 patients died (p less than 0.01, modified Fisher's exact test). An additional retrospective study on the relation between heparin treatment and ICH in SVT patients was based on 102 patients, 43 of whom had an ICH. 27 of these patients were treated with dose-adjusted, intravenous heparin after the ICH. Of these 27 patients, 4 died (mortality 15%), and 14 patients completely recovered. Of the 13 patients that did not receive heparin after ICH, 9 died (mortality 69%) and only 3 patients completely recovered. We conclude that anticoagulation with dose-adjusted intravenous heparin is an effective treatment in patients with SVT and that ICH is not a contraindication to heparin treatment in these patients.