BACKGROUND Pressure ulcers (PUs) in the sacral region can be a complication of surgical procedures performed in the lithotomy position. Previous reports have noted a difference between men and women in PU development related to the supine position, and body weight and body mass index (BMI) have been also described as known risk factors in supine position-related PU development. The BIG-MAT® system is a noninvasive pressure distribution measurement device used to measure external pressure (EP). We used this system to investigate the relationship between EP to the sacral region in the lithotomy position and selected physical characteristics. METHODS We recruited 21 young, healthy volunteers (11 men and 10 women, aged 21.4±0.5 years). Using the BIG-MAT system, we measured four types of EP to the sacral region: box pressure, peak box pressure, contact pressure, and peak contact pressure. We analyzed the relationships between these dynamic parameters and physical characteristics of the participants. RESULTS There were no differences between men and women in the four types of EP, and no significant differences related to the participants' height, weight, or BMI. CONCLUSION An individual's height, weight, and BMI may not contribute to the risk of inducing lithotomy position-related PUs in the sacral region. The noninvasive pressure distribution measurement system BIG-MAT for patients in the lithotomy position during surgery could become a significant device when estimating EP at the sacral region.