This retrospective study analyzed the results of 26 porous-coated anatomic unicompartmental knee arthroplasties to determine the failure rate, the mode of failure, and the presentation of the failure. The mean follow-up was 6.9 years. All patients were assessed using the American and Oxford knee scores. The revision rate was 42%4, with a mean revision time of 38.4 months. The commonest presentation of failure included pain (100%), decreased mobility (75%), swelling (58%), and giving way (50%). The commonest modes of failure included femoral loosening (55%), polyethylene wear (55%), loosening and polyethylene wear (72%), and fracture-dislocation of the femoral prosthesis (18%). The 42% failure rate of the porous-coated anatomic unicompartmental knee arthroplasty necessitates regular surveillance and prompt revision, if failing, to avoid osteolysis.