Jellyfish envenomations are common amongst temperate coastal regions and vary in severity depending on the species. Stings result in a variety of symptoms and signs, including pain, dermatological reactions and, in some species, Irukandji syndrome (including abdominal/back/chest pain, tachycardia, hypertension, sweating, piloerection, agitation and sometimes cardiac complications). Many treatments have been suggested for the symptoms and signs of jellyfish stings. However, it is unclear which interventions are most effective. To determine the benefits and harms associated with the use of any intervention, in both adults and children, for the treatment of jellyfish stings, as assessed from randomised trials. We searched the following electronic databases in October 2012 and again in October 2013: the Cochrane Central Register of Controlled Trials (CENTRAL;The Cochrane Library, Issue 9, 2013); MEDLINE via Ovid SP (1948 to 22 October 2013); EMBASE via Ovid SP (1980 to 21 October 2013); and Web of Science (all databases; 1899 to 21 October 2013). We also searched reference lists from eligible studies and guidelines, conference proceedings and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) and contacted content experts to identify trials. We included randomised controlled trials that compared any intervention(s) to active and/or non-active controls for the treatment of symptoms and signs of jellyfish sting envenomation. No language, publication date or publication status restrictions were applied. Two review authors independently conducted study selection and data extraction and assessed risk of bias using a standardised form. Disagreements were resolved by consensus with a third review author when necessary. We included seven trials with a total of 435 participants. Three trials focused on Physalia (Bluebottle) jellyfish, one trial on Carukia jellyfish and three on Carybdea alata (Hawaiian box) jellyfish. Two ongoing trials were identified.Six of the seven trials were judged as having high risk of bias. Blinding was not feasible in four of the included trials because of the nature of the interventions. A wide range of interventions were assessed across trials, and a wide range of outcomes were measured. We reported results from the two trials for which data were available and reported the effects of interventions according to our definition of primary or secondary outcomes.Hot water immersion was superior to ice packs in achieving clinically significant (at least 50%) pain relief at 10 minutes (one trial, 96 participants, risk ratio (RR) 1.66, 95% confidence interval (CI) 1.01 to 2.72; low-quality evidence) and 20 minutes (one trial, 88 participants, RR 2.66, 95% CI 1.71 to 4.15; low-quality evidence). No statistically significant differences between hot water immersion and ice packs were demonstrated for dermatological outcomes.Treatment with vinegar or Adolph's meat tenderizer compared with hot water made skin appear worse (one trial, 25 participants, RR 0.31, 95% CI 0.14 to 0.72; low-quality evidence).Adverse events due to treatment were not reported in any trial. This review located a small number of trials that assessed a variety of different interventions applied in different ways and in different settings. Although heat appears to be an effective treatment for Physalia (Bluebottle) stings, this evidence is based on a single trial of low-quality evidence. It is still unclear what type of application, temperature, duration of treatment and type of water (salt or fresh) constitute the most effective treatment. In addition, these results may not apply to other species of jellyfish with different envenomation characteristics. Future research should further assess the most effective interventions using standardised research methodology.