We evaluated the safety and clinical effect of the low-molecular-weight heparin dalteparin in 60 consecutive patients with acute ischemic cerebrovascular disease. The indication for dalteparin therapy was stable cardioembolic stroke in 24 patients, stroke in progression in 23 patients, and serious and frequent TIAs or TIAs despite aspirin in 13 patients. The mean age was 73.0 years (49–85). After exclusion of hemorrhage by cerebral CT scan, dalteparin therapy was started 39 h (2–168) after onset of symptoms. Dalteparin was administered as subcutaneous injections 100 IU/kg body weight every 12 h with a mean daily dose of 13,533.4 IU and a mean duration of 8.7 days (3–16). In patients with TIAs and cardioembolic stroke, there were no further cerebrovascular episodes or clinical deterioration. Clinical worsening occurred in a total of 6 patients (10%), all 6 included because of progressive stroke. Cerebral CT excluded hemorrhagic transformation as reason for deterioration. A second CT was done in all patients after a mean duration of 7.8 days (5–11) of dalteparin therapy and revealed asymptomatic hemorrhagic transformation in 3 patients (5.0%). All these 3 patients had taken aspirin prior to dalteparin therapy. There was no clinical significant decrease in hemoglobin values or platelet count during dalteparin therapy. We conclude that anticoagulant therapy with weight-adjusted doses of the low-molecular-weight heparin dalteparin in patients with acute ischemic cerebrovascular disease is safe in this setting and that the clinical effect should be studied in randomized