BACKGROUND: Isolated involvement of the medial compartment of the knee in degenerative disease is encountered in about 25% of patients with gonarthrosis. We aim to show that in a well-selected group of such patients, medial unicompartmental knee arthroplasty (UKA) is a good option. OBJECTIVES: Review the functional outcomes of patients undergoing UKA and determine the long-term survivorship of the implants and complications of the procedure. DESIGN: Analytical retrospective chart review. SETTING: Academic tertiary care medical center and tertiary care private hospital in the western region of Saudi Arabia. PATIENTS AND METHODS: We selected patients who underwent medial UKAs by the same surgeon between December 1988 and December 2009. The life table approach and the Kaplan-Meier statistical method were used to estimate the survival rate (5–30 years) with revision as the endpoint. Functional outcome scores were determined according to the Knee Society Clinical Rating System. MAIN OUTCOME MEASURES: Change in performance scores for pain, walking, and range of movement. Survivorship of the implants with removal of the implant as the endpoint; post-operative complications. SAMPLE SIZE: 218 implants on 142 patients. RESULTS: The survival rate for UKA was 94.7% at 10 years (95% CI 0.906–0.970), 80.9% at 20 years (95%CI 0.724–0.871), and at 30 years it was 77.8% (95%CI 0.669–0.855) of the total knee arthropathies. The average grand total functional score increased from 61 (maximum 200) at 0 months to above 150 at ≥6 months. CONCLUSION: UKA is a good option for isolated medial compartment gonarthrosis with excellent functional outcome and good survivorship in selected patients. LIMITATION: Single center experience, retrospective. We lost 6.0% of patients during follow-up. CONFLICT OF INTEREST: None.