Thirty-two unicondylar knee replacements in thirty patients were done between 1972 and 1974. Ten patients were lost to follow-up because of death or other reasons. The remaining twenty-two knees (seventeen medial and five lateral compartments replaced) had a follow-up ranging from five to seven years, with an average of six years. Although the quality and result of these unicondylar arthroplasties were initially considered good, they have subsequently shown a marked deterioration. At the time of this report only one knee was rated as excellent; seven knees, as good; four knees, as fair; and ten knees, as poor. Seven knees (28 per cent) have been converted to a bicondylar prosthesis. The lateral replacements did much better than the medial replacements.