A retrospective review with a mean follow-up time of 60 months was performed on 126 patients who had treatment of unicompartmental gonarthrosis with either abrasion arthroplasty plus arthroscopic debridement or arthroscopic debridement alone. Fifty-nine patients had abrasion arthroplasty and arthroscopic debridement, and 67 patients had arthroscopic debridement alone. All patient had stage II Ahlbäck changes roentgenographically, as well as Outerbridge stage IV changes arthroscopically in the involved compartment. All the knees were evaluated postoperatively at a minimum of 60 months, utilizing The Hospital For Special Surgery Knee Scoring System. In the group treated with abrasion arthroplasty, 51% had good to excellent results, 16% had fair results, and 33% had poor results. The conditions of ten of the patients who had poor results actually became worse subsequent to their abrasion arthroplasty. In the group that had arthroscopic debridement, 66% had good to excellent results, 13% had fair results, and 21% had poor results. The conditions of 12 of the patients who had poor results actually became worse subsequent to the arthroscopic debridement.