Objective: Headache occurs in 10-15% of COVID-19 patients. The optic nerve sheath diameter (ONSD) is an indirect measurement of the intracranial pressure (ICP). This study aimed to determine whether there was a relationship between ICP and headache in COVID-19 patients by measuring the ONSD. Methods: The study included a total of 91 people: 68 COVID-19 patients and 23 healthy volunteers as a control group. The two groups were first compared in terms of the ONSD using the ultrasonography (US) technique. Second, the severity of headache in the COVID-19 group was numerically evaluated (from 0 to 10) and the group was then divided into low, moderate, and high subgroups according to headache severity. Afterwards, the ONSD measurements of participants in the COVID-19 group were compared in between the subgroups. Results: We found that the COVID-19 patients had higher ONSD levels than healthy controls (4.7±0.7 mm vs. 4.1±0.4 mm, p <0.001). In the COVID-19 patients, there was a significant difference of ONSD levels between the low and moderate as well as the low and high groups. However, no significant difference was observed between the moderate and high groups. There was also a positive correlation between the headache intensity and ONSD diameter level (p=0.01 r=0.39). Conclusion: COVID-19 patients with headache had higher ONSD levels than healthy volunteers, consistent with increased intracranial pressure. The latter may be one of the causes of headache in COVID-19.