In a controlled study using 15 piglets, the efficacy of skin stretching using a skin stretching device was tested by quantifying the tension decrease during skin stretching in undermined and not undermined wounds. The viability of the skin margins was examined in both situations. Thirty standardized wounds was created: around 15 wounds on one flank, the surrounding skin was undermined; whereas around the 15 wounds on the opposite flank, the surrounding skin was not undermined. The force required to close the 9 x 9 cm defect was measured at the beginning, after undermining, and after 30 minutes of skin stretching. Also examined was the wound healing after 1 day and 1 week. A tension decrease of 3.02 N (13.6 percent reduction of the total force that is required to close the wound at the beginning) was seen due to undermining the surrounding skin. Skin stretching for 30 minutes without undermining the skin showed a tension decrease of 6.10 N (26.5 percent). Therefore, the tension decrease due to skin stretching was twice as high in comparison with undermining the skin margins alone. This has been statistically proven to be significant (-d (difference) = 3.08, 95 percent confidence interval = 2.16; 4.00, p < 0.001). When the undermined skin of the wound was stretched for 30 minutes, we measured a total tension decrease of 7.60 N (34.1 percent). There was a statistically significant but small difference in total tension decrease as a result of undermining combined with skin stretching in comparison with skin stretching without undermining (-d = 1.51, 95 percent confidence interval = 0.77; 2.23, p < 0.001). Undermining the surrounding skin involved cutting musculocutaneous perforating vessels. Looking at the viability of the skin, seven wounds, all found in the undermined group, showed skin necrosis after 1 week. Excessive seroma formation was seen in all wounds around which the skin was undermined. In the not undermined wounds, there were no problems in wound healing. In conclusion, skin stretching for only 30 minutes using a skin stretching device significantly reduces wound closing tension. The additional advantage of skin stretching over that of undermining alone is clearly shown. Undermining the wound margins before skin stretching gives a small additional tension decrease but has well-known complications, such as skin-edge necrosis and seroma formation.