By means of an ultrasonic technique, skin thickness was measured in 13 women subjected to mammary reconstruction by tissue expansion. Measurements were performed the day before introduction of the expander, after the last inflation, the day before introduction of the permanent implant, and at 2 weeks and 6 months after this operation. Five patients had their expanders inflated every day (rapid expansion), and 8 patients, once a week (slow expansion). A decrease in skin thickness during the inflation period was recorded, and this decrease was permanent even 6 months after the second operation. After exchange of the expander for a permanent implant, there was a transient statistically significant increase in skin thickness. There was no statistical difference between the groups of rapid and slow expansion.