PURPOSE To determine the type, incidence, and clinical outcomes of severe complications from strabismus surgery in the United Kingdom. METHODS Cases were identified prospectively through a national surveillance unit between September 1, 2008, and August 31, 2010. Questionnaire data were requested at the time of the complication recognition and at 6 months' follow-up. Outcome was graded I to V, with a poor or very poor outcome meaning either loss of corrected visual acuity or primary position double vision. RESULTS A total of 60 completed reports of adverse events and complications were received during the study period. During the same time approximately 24,000 strabismus surgeries were performed in the United Kingdom, yielding an overall incidence of 1 in 400 operations (95% binomial confidence, 1 per 333-500 operations). The most common reported complication was perforation of the globe (19 [0.08%]), followed by a suspected slipped muscle (16 [0.067%]), severe infection (14 [0.06%]), scleritis (6 [0.02%]), and lost muscle (5 [0.02%]). Overall, complications were reported in adults and children in equal numbers; however, scleritis was significantly more common in adults. A poor or very poor clinical outcome was recorded as 1 operation per 2,400. CONCLUSIONS This study provides an assessment of the overall risks associated with strabismus surgery in the United Kingdom. Complications with the potential for a poor outcome are relatively common, but the final clinical outcome is good in the majority of cases. (J AAPOS 2013; 17:59-63)