Aims: To study functional outcome and survivorship of custom designed knee implants for primary and revision TKR where off-the-shelf prostheses were unsuitable. Methods: Clinical and radiological results of twenty-three custom-designed total knee prosthesis in twenty patients were prospectively reviewed. The indications were bone loss following multiple revisions of total knee prosthesis and debridement for infection, periprosthetic fractures, bone deformity with rickets and small bones with juvenile chronic arthritis. All implants designed and manufactured at Centre for Biomedical Engineering, Stanmore, U.K. Four different designs of knee prosthesis used: Condylar knee of miniature size, CAD-CAM knee, Superstabiliser and Rotating Hinges. Hospital for Special Surgery (HSS) score taken preoperatively, at 3 months, and yearly by an independent research physiotherapist. Duration of follow up: 62.5 months (28–126 months) Results: Average HSS score improved from 13.5 points (range 0–48) pre-operatively to 86.5 points postoperatively (range 62–96) (p=0.025). Average maximum flexion post operatively: 86.4° (range 60°–122°). Sixteen knees had excellent, five good and two poor results. Extension lag of 15°–25° in three patients. One patient with juvenile chronic arthritis needed revision at five years after index arthroplasty. Conclusions: Clinical and radiological results for custom designed prostheses compare favourably with standard knee prosthesis for similar indications. Our results support the use of a custom designed knee implant as salvage prosthesis and also as an alternative to arthrodesis or amputation.