Relevance. Diffuse-type tenosynovial giant cell tumor (D-TGCT) is a relatively rare tumor of tendon sheaths and synovial membranes, but its appearance significantly impairs organ function. Currently, the pathogenesis of this disease is associated with overexpression of colony stimulating factor-1.Intention: To show the possibilities and advantages of radical resection of D-TGCT of the knee joint with arthroscopic access before traditional open surgery.Methodology. In hospital # 2 of the All-Russian Center for Emergency and Radiation Medicine named after A.M. Nikiforov, EMERCOM of Russia (St. Petersburg), two female military personnel aged 31 and 38 years underwent arthroscopic surgeries on the knee joint for radical resection of D-TGCT in 2018. Dynamic magnetic resonance imaging (MRI) and histological examination of puncture biopsy specimens were conducted preoperatively. Functionality of the knee joints was assessed before surgery and in the long term using Knee injury and osteoarthritis outcome score (KOOS), Lysholm Knee Scoring Scale (Lysholm) and visual analogue scale (VAS) and MRI control.Results and Discussion. D-TGCTs of the knee joints were removed simultaneously and radically using arthroscopic access. Histological examination of the obtained samples revealed the giant-cell diffuse-type tumors in both cases. A stable remission of the disease was obtained in the long-term period of postoperative observation. Good cosmetic surgery results have been achieved. The average KOOS, Lysholm, and VAS scores for knee function in patients were consistent with excellent and good results.Conclusion. The long-term results of surgical treatment of D-TGCT of the knee via arthroscopic access showed that the procedure can be reliable, safe and beneficial for functionality.