Introduction: Headache is one of the most important complaints in emergency room (ER) admissions, and the rate of the increase in intracranial pressure in these cases should not be overlooked. This study was performed to investigate the value of the measurement of optic nerve sheath diameter (ONSD) by ocular ultrasound in ER patients with the complaint of headache and increase in intracranial pressure regarding this. Materials and Methods: A total of 100 patients who applied to the ER with the complaint of headache were included in this prospective study. Fifty patients with increased ONSD (= 5 mm) and 50 patients with normal ONSD (< 5 mm) were obtained. ONSD measurements were performed with 7.5-10 MHz linear probe and closed-eye technique. In addition to this, all patients underwent cranial computerized tomography (CT) examinations, and CT results were compared with the results of the ocular ultrasound. Results: The median right and left ONSD values were detected to be 4.3 mm (3.6-5.5 mm) and 4.4 mm (3.6-5.6 mm) in patients whose cranial CT results were within normal limits. However, the median right and left ONSD values were detected to be 5.5 mm (5.1-6.3 mm) and 5.5 mm (5.1-6.4 mm) in patients whose cranial CT examination results were abnormal. In all cases with abnormal CT findings, the right and the left ONSD measurements were significantly higher (P < 0.001). Furthermore, ONSD value in the ipsilateral side with the lesion was significantly higher than the contralateral side (P < 0.001). Conclusion: Bedside ocular ultrasound is a noninvasive and easily applicable method in ER for the detection and evaluation of intracranial hypertension with headache.