In order to meet the requirements of large defects created by sacral and trochanteric pressure ulcers, tensor fasciae latae and lumbosacral fasciocutaneous flaps were expanded with a silicone expander in six patients (10 flaps). In 8 of the flaps the location of pressure ulcers was trochanteric, and in 2 it was sacral. In each case the period of expansion was 4 weeks. Histopathologic examination after expansion showed an increase in the vascularity and overall thickness of fascia in both types of flaps. After 4 weeks of expansion, the perifascial areolar tissue was replaced with thick granulation tissue in the tensor fasciae latae flaps. This markedly vascular layer of granulation tissue interposed between the fasciae and the subcutaneous tissue augmented the internal matrix of the flap, thereby lowering the potential for shearing during flap elevation. Conceivably, owing to the absence of an areolar tissue layer in the lumbosacral fasciocutaneous flaps, no layer of granulation tissue was observed. The average thickness of the fibrous capsule formed around the expanders was 573.2 microns, which was composed of three structurally different zones. Prior tissue expansion obviously assisted primary closure of the flap donor site. In addition, it seems that the tissue-expansion process rendered the distal portion of fascial flaps more robust because of increased vascularity. It is therefore proposed that preparatory tissue expansion of fascial flaps has several advantages. The obvious benefits include the ability to close larger defects while closing the donor site primarily. As a result of this study, the additional benefits may include a reduction in the mechanical shear potential of these flaps and an improvement in their vascularity.