OBJECTIVE To examine the safety and efficacy of disinsertion of the inferior oblique muscle in the treatment of long-standing ipsilateral superior oblique paresis. METHODS This retrospective study included 52 patients who underwent disinsertion of the inferior oblique muscle over a 5-year period. Mean age at presentation was 30.8 years (range: 1-70 years). All patients had long-standing unilateral superior oblique paresis and overaction of the ipsilateral inferior oblique muscle. Information recorded included pre- and postoperative vertical deviation, pre- and postoperative Hess chart error scores, reoperation rate, and symptom relief. RESULTS Following surgery, mean vertical deviation was reduced from 12.9 to 4 prism diopters, while mean Hess chart error score decreased from 596 to 258. This procedure alone resulted in satisfactory symptom relief in 84.6% of patients. The only complication was significant undercorrection requiring further surgery in 13.6% of patients and prisms in 1.8%. When further surgery was needed, the procedure of choice was tucking of the affected superior oblique. Recession of the contralateral inferior rectus was carried out when superior oblique tucking was believed to be unsuitable. CONCLUSIONS Disinsertion of the inferior oblique muscle is a safe and effective treatment for the majority of long-standing idiopathic unilateral superior oblique pareses.