A deep tissue pressure injury (DTPI) is a serious type of pressure injury that begins in the muscle closest to the bone and may not be visible in its early stages. Its hallmark is rapid deterioration despite the use of appropriate preventive interventions. In 2007, the National Pressure Ulcer Advisory Panel added suspected deep tissue injuries to the traditional classification system, and by 2010 DTPIs had accounted for about 9% of all pressure injuries and were for the first time more prevalent than stage 3 or 4 pressure injuries. On average, patients who develop these injuries are older and have a lower body mass index than patients who develop other pressure injuries. Most commonly, DTPIs appear on the skin over the coccyx or sacrum, the buttocks, and the heels. This article discusses the pathophysiology; risk factors; and assessment, prevention, and treatment of DTPIs, using a composite case to illustrate the progression of this serious type of pressure injury.