The aim of this prospective follow-up study was to determine if gait measurements and/or clinical measurements could detect differences in treatment outcome between two surgical interventions in patients with knee osteoarthritis (OA). The patients were followed for 5 years after surgery. Forty patients, 55-70 years of age, with unilateral knee OA were included. The patients were treated either with a high tibial osteotomy (HTO) (n=18) or a unicompartmental knee arthroplasty (UKA) (n=22). Clinical outcome measures were the British Orthopaedic Association (BOA) score, pain during walking, passive range of knee motion (PROM) and patients' subjective opinion. The gait variables were free walking speed, step frequency, step length and single and double-stance phase for each leg. The patients were examined before surgery and 3 months, 1 year and 5 years after surgery. The time-distance variables of gait could detect differences in treatment outcome, 3 months after surgery, while the clinical outcome measures, as given here, could not detect any differences between the two groups of patients. Measurements of free walking speed could be recommended for clinical evaluation, after surgical interventions, in patients with knee OA.