OBJECTIVE To determine the effectiveness of a standard fixed 10 mm inferior oblique (IO) recession with or without vertical rectus recession in visually mature patients with unilateral superior oblique paresis (SOP) and mild to moderate IO overaction. METHODS The records of 24 patients over 12 years of age who had 10 mm IO recession for SOP, for IO overaction of +1 to +3 (out of maximum +4), with 6+ months of followup were reviewed. Criteria required for a "successful" outcome included: 1. hyperdeviation of 5delta or less in primary position; 2. elimination of any compensatory abnormal head posture; and 3. elimination of diplopia in the central 30 degrees of the binocular visual field. RESULTS In 16 cases of IO recession alone, 88% were "successful" and in 8 cases who had in addition either contralateral inferior rectus recession or ipsilateral superior rectus recession, 75% were "successful". IO 10 mm recession alone led to an average reduction of 9.1 PD of hypertropia in primary position. CONCLUSIONS A standard ungraded 10 mm recession of the IO alone or in combination with vertical rectus muscle recession is an effective weakening procedure with a high success rate for patients with unilateral SOP with mild to moderate IO overaction. In occasional cases of undercorrection, a subsequent IO myectomy is very feasible and effective.