Bedside ultrasonographic measurement of optic nerve sheath diameter (ONSD) has been proposed as a method to detect raised intracranial pressure (ICP) in various clinical settings. The aim of our study is to evaluate the use of ultrasonography in the case of intracranial hemorrhage and to assess the validity of the conventional cut-off point of 5 mm. A prospective blind observational study in a 10-bed multivalent intensive care unit was carried out by enrolling 53 adult patients with primary intracerebral hemorrhage (23) or subarachnoid hemorrhage (30), requiring ICP monitoring, sedation, and mechanical ventilation and 53 control patients with no intracranial pathology, requiring sedation and mechanical ventilation. ONSD was measured 3 mm behind the globe by using a 7.5 MHz linear ultrasound probe. Mean binocular ONSD was used for data analysis. Nineteen patients proved to have raised ICP (>20 mm Hg). In this group, ONSD at admission was 6.2+/-0.6 mm, a significantly higher value than in low ICP patients (P<0.01). In the 34 patients with ICP <20 mm Hg, ONSD was 5.0+/-0.5 mm, and it resulted not significantly different from ONSD in the control group (4.9+/-0.4 mm). A receiver operator characteristic curve was constructed and an ONSD threshold of 5.2 mm as a predictor of ICP >20 mm Hg proved to be an attractive combination of sensitivity and specificity (94% and 76%, respectively). In conclusion, our study confirms the utility of optic nerve ultrasound in the early diagnostic evaluation of patients with known or suspected intracranial hemorrhage.