BACKGROUND: The use of botulinum toxin as an investigative and treatment modality for strabismus is well reported in the medical literature. However it is unclear how effective its use is in comparison to other treatment options for strabismus. OBJECTIVES: To evaluate the efficacy of botulinum toxin in the treatment of strabismus compared with alternative treatment options, to investigate dose effect and complication rates. SEARCH METHODS: We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2011, Issue 11), MEDLINE (January 1950 to December 2011), EMBASE (January 1980 to December 2011), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to December 2011), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). There were no date or language restrictions in the electronic searches for trials. The electronic databases were last searched on 5 December 2011. We manually searched the Australian Orthoptic Journal and British and Irish Orthoptic Journal and ESA, ISA and IOA conference proceedings. We attempted to contact researchers who are active in this field for information about further published or unpublished studies. SELECTION CRITERIA: We included randomised controlled trials (RCTS) of any use of botulinum toxin treatment for strabismus. DATA COLLECTION AND ANALYSIS: Each review author independently assessed study abstracts identified from the electronic and manual searches. Author analysis was then compared and full papers for appropriate studies were obtained. MAIN RESULTS: We found four RCTs that were eligible for inclusion. Two trials found that there was no difference between the use of botulinum toxin and surgery for patients requiring retreatment for acquired esotropia or infantile esotropia. There was no evidence for a prophylactic effect of botulinum toxin in a treatment trial of acute onset sixth nerve palsy. Botulinum toxin had a poorer response than surgery in a trial of patients requiring treatment for horizontal strabismus in the absence of binocular vision. Reported complications included ptosis and vertical deviation and ranged from 24% in a trial using Dysport™ to 52.17% and 55.54% in trials using Botox™. AUTHORS' CONCLUSIONS: The majority of published literature on the use of botulinum toxin in the treatment of strabismus consists of retrospective studies, cohort studies or case reviews. Although these provide useful descriptive information, clarification is required as to the effective use of botulinum toxin as an independent treatment modality. Four RCTs on the therapeutic use of botulinum toxin in strabismus have shown varying responses ranging from a lack of evidence for prophylactic effect of botulinum toxin in acute sixth nerve palsy, to poor response in patients with horizontal strabismus without binocular vision, to no difference in response in patients that required retreatment for acquired esotropia or infantile esotropia. It was not possible to establish dose effect information. Complication rates for use of Botox™ or Dysport™ ranged from 24% to 55.54%.