Although many weakening procedures for the inferior oblique muscle have been advocated, there is some controversy as to the most beneficial procedure for weakening overacting inferior oblique muscles. This study was undertaken to determine if unilateral anterior transposition of the inferior oblique muscle alone could be a safe and effective procedure for treating unilateral superior oblique palsy from the perspective of hypertropia, inferior oblique overaction, and abnormal head posture. The records of 33 patients, who underwent anterior transposition of the inferior oblique muscle for unilateral superior oblique palsy at our institution between Jan 1995 and Dec 2002, were retrospectively reviewed. The average preoperative inferior oblique overaction was 2.3 +/- 0.64, and the hypertropia in the primary position was 12.3 +/- 7.69 prism diopter (PD). Twenty-six patients showed head tilt to the opposite direction preoperatively. After the anterior transposition of the inferior oblique, inferior oblique overaction was diminished in 32 patients (97%). Twenty-six out of 33 patients (79%) had no hypertropia in the primary position at last postoperative assessment. Of the 26 patients with head tilt before surgery, 21 patients (81%) achieved full correction after surgery. Satisfactory results were obtained in most of the patients in our study with the exception of three patients who required additional surgery. No patient demonstrated postoperative hypotropia in the primary position. None of the patients noticed elevation deficiency or lower lid elevation. The anterior transposition of the inferior oblique was found to be safe and effective for treating superior oblique palsy with secondary overaction of the inferior oblique muscle.