Objective: The authors performed an experimental and a prospective clinical study to evaluate the histological and magnetic resonance imaging (MRI) alterations after irradiation of meniscus using holmium:YAG (Ho:YAG) laser VersaPulse Select 60 watts and InfraTome Delivery Systems 30 degrees Handpiece (spot size at fiber tip 0.4 mm; Coherent Medical, Palo Alto, CA). Background Data: Recently, some authors reported a few cases with articular cartilage damage or paraarticular osteonecrosis following arthroscopic knee surgery in which the laser was used to assist in the treatment of meniscal pathology. Methods: Meniscus specimens in saline immersion were exposed to Ho:YAG laser irradiation. The laser wavelength was 2.1 mum and pulse duration was 250 mu sec. Power settings were 1-1.5 joules per pulse and 10-15 Hz. Total laser energy used in these procedures was 2, 3.5, and 6 K joules. Eight patients with meniscal problems underwent arthroscopic partial meniscectomy using Ho:YAG laser. Total laser energy used for these surgeries was 1.5-2.5 K joules. MRI was performed preoperatively and at 6 months postoperatively. Results: At higher energy levels (more than 3 K joules), separation of the gap between the collagen fibers, and a three-dimensional dispersion in the striation were observed on electron microscopic evaluation of meniscus specimens. No patient had abnormal signals in MRI (a sign of articular cartilage damage or osteonecrosis) following arthroscopic laser surgery. Conclusion: When higher energy level is required, conventional instruments should be preferred in the treatment of meniscal lesions. Laser should be reserved for the posteriorly located and smaller meniscal lesions.