Summary. Since the early studies on decubitus many authors expect significant influence of shear on decubitus risk. In the study described here skin oxygen tension at the sacrum was measured with combined pressure and shear stress on a young healthy population (mean age 25‐5 years, SD 3–4 years). Cut‐off pressure is defined as the level of external pressure exerted on the skin at which the skin oxygen tension is 1–3 kPa. At this level ischaemia of the skin can be expected (Bar, 1988). A mean cut‐off pressure of 11‐6 kPa was found when no shear stress was applied vs. a significantly lower mean cut‐off pressure of 8‐7 kPa with a shear stress of 3‐1 kPa. No significant relationship was found between cut‐off pressure and systolic blood pressure, diastolic blood pressure, skin thickness at the sacrum, percentage of fat and skin oxygen tension in the unloaded situation.,