To determine the role of unicompartmental knee replacement in knee arthroplasty and, in particular, the design and function of the ICLH (Finsbury Prosthetics Ltd., London, UK) knee prosthesis, the authors report their experience with 18 patients (15 women and 3 men, mean age 73 years), who underwent unicompartmental knee replacement with this prosthesis. The prosthesis failed in five (27.8%) cases, but in the remainder the results were good to excellent over a follow-up extending to 6 years (mean 4.5 years). The main problem with the ICLH prosthesis is the linear wear of the plastic of the tibial component, caused by a sharp radius at the edge of the femoral component. This leads to fracture and breakdown of the tibial portion. Because the short-term results are good but the long-term results are poor, the authors suggest that the ICLH unicompartmental knee prosthesis should be reserved for use in patients whose life expectancy is short.