Background <p>Liposuction surgery is often performed with patients either in a supine or prone position. The prone position can potentially increase the intracranial pressure, with the risk of adverse outcomes. Ultrasound can be used to measure the optic nerve sheath diameter (ONSD), which is a validated non-invasive marker for assessing intracranial pressure changes. However, the use of ultrasound to measure the ONSD has not been previously reported in liposuction surgery.</p> Methods <p>A prospective clinical trial was conducted in patients undergoing liposuction. Eligible patients were assigned to either a prone position group or supine position group. The patients’ ONSD and vital signs levels were recorded at various time points, namely upon awakening, 30 min, and 60 min after anesthesia induction, and immediately before the conclusion of surgery while in the supine position. The incidence of 24-hour postoperative nausea and vomiting (PONV) was also recorded.</p> Results <p>In total, 47 patients were included in the study and were assigned to a prone group (25 patients) or supine group (22 patients), respectively. In the prone group, the ONSD values were higher at 30 min and 60 min after anesthesia than before anesthesia (<i>p </i>&lt; 0.05). Compared with the supine group, the prone group had a significantly enlarged ONSD after anesthesia (<i>p </i>&lt; 0.05). There was no statistically significant difference in PONV between the two groups.</p> Conclusion <p>Ultrasound can be used to dynamically monitor the ONSD during liposuction. Patients in the prone position had a statistically significant increased ONSD compared with those in the supine position.</p> Level of Evidence II <p>This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors <a href="https://www.springer.com/00266">www.springer.com/00266</a>.</p>