Tissue expansion generates metabolic and morphological changes in the expanded tissues. The alteration of epidermal and dermal thickness has been investigated in many animal studies, but few human studies have been published. We have studied 11 women whose breasts were reconstructed with tissue expansion after mastectomy. The expanded breast skin was biopsied on three occasions: before expansion, at the time of maximal expansion, and six months after the completed reconstruction. Specimens were prepared for light microscopy and epidermal thickness was assessed. There was a significant increase in epidermal thickness (p < 0.05) at the time of maximal expansion. The values before and at six months after reconstruction were not significantly different from each other. We conclude that the epidermis increases in thickness as a result of expansion and returns to normal thickness six months after cessation of expansion.