For the purpose of investigating the clinical efficacy of a newly designed wedged insole, 149 patients with medial osteoarthritis of the knee were followed from one year to five years and five months. A rating system for pain, walking ability, and both were used for evaluation of the clinical results. Comparing two groups consisting of 107 patients with early radiographic stages (Stage I or II), 67 patients (Group I) treated with both a wedged insole and anodyne (Indomethacin 600 mg/day) showed a significantly greater improvement than 40 patients (Group II) treated with anodyne alone. Analyzing the therapeutic efficacy of the wedged insole according to the radiographic stage, the prescription of a wedged insole was significantly more effective for patients with mild osteoarthritis (Stages I, II, and III), and ineffective for those with advanced osteoarthritis (Stage IV). The wedged insole, designed on the basis of an established hypothesis, represents an excellent means of conservative treatment for early medial osteoarthritis of the knee.