Purpose - retrospective analysis of the causes of complications after knee replacement in tumor lesions depending on the type of implants and classification of complications by severity. Material and methods. The outcomes of operations of knee replacementin tumor lesions performed in 161 patients in the period between 1993 and 2012 were studied. All patients were divided into two groups. The first group included 68 (42.2%) patients, whom the Russian endoprostheses were implanted. The second group included 93 (57.8%) patients, who were operated using modern foreign endoprostheses. Results. 74 (45.9%) patients underwent revision surgery due to the complications in different terms after primary oncologic replacement, with 67 (90.5%) requiring a removal of the primary endoprosthesis. By severity, all complications were divided into 5 types. Infections were the most frequent complications of knee replacement resulting in revision surgery (19 cases, 25.7% of all revision operations). Conclusion. Improvement of oncological systems quality lead to the decrease in the rate of revision surgery due to mechanical reasons. However, the complication rate after knee replacement remains higher than after conventional arthroplasty.