The authors present an account of a group of 51 patients to whom an individual endoprosthesis of the knee joint was implanted on account of a tumour. A primary bone tumour was involved in 42 cases and a metastatic process in 9 cases. Twenty-four endoprostheses were cemented, 26 were implanted without cement. The mean follow-up period was 43 months. Functional results excellent and good in 61%, poor results only in 5%.