In many clinical and in vitro studies, the effect of laser radiation on meniscal tissue was examined. Clinical studies referred to clinical criteria like swelling, effusion, and pain to evaluate laser effects. In vitro studies showed the laser effect in the moment of cutting the tissue. But the effect of laser radiation on biological tissue also depends on the vital reaction of the tissue. So, the real extent of tissue damage caused by laser irradiation can only be examined in long-term in vivo studies. This was the purpose of this study. Seventy-two knees of pigs underwent arthroscopic meniscal cuts in the anterior horn of the medial meniscus. The pigs were divided into 6 groups: The first 5 groups were operated with 5 different laser systems: Neodym: YAG 1,440-nm wavelength; Nd:YAG 1,064-nm wavelength, Excimer, Holmium:YAG, and CO2. The sixth group was operated with mechanical punches. From each group, the menisci of the pigs were examined macroscopically and by light-microscope after survival periods of 0, 2, 6, 12 weeks. Results were as follows. (1) All laser systems caused greater damage to the meniscal tissue than mechanical instruments. (2) This damage was a biological reaction of the tissue, characterized by a necrotic zone surrounding the meniscus cut. (3) This necrotic zone was not visible intraoperatively but only 2, 6 and 12 weeks after operation. The diameter of the necrotic zone ranged between 1.5 nm and 9 mm. (4) Meniscus cuts with mechanical instruments showed no necrotic zone in the surrounding tissue. (5) Laser cuts in the meniscus caused more extensive healing reaction than cuts with mechanical instruments. (6) The quality of this healing reaction varied with the different laser systems: the Nd:YAG 1,064-nm, Ho:YAG, and CO2 laser caused only an incomplete healing because the tissue repair showed by tissue growing from the synovial edge into the defect only. The Nd:YAG 1,440-nm wavelength and Excimer led to tissue growing from the synovial edge and to remodeling of original meniscal tissue, recognizable by reduction of the necrotic zone. Arthroscopic surgeons should be aware that the damage to meniscus tissue caused by a laser is much greater than can be seen intraoperatively and is much greater than the damage caused by mechanical punches. The healing reaction of the tissue is more extensive after laser application than after use of mechanical instruments. Results of in vitro studies on the tissue damage caused by lasers are insufficient to describe the whole extent of laser effects on living tissue.