Abstract OBJECTIVES: The present study is a meta-analysis of clinical studies conducted to evaluate the efficacy of oximes in the treatment of organophosphorus (OP) intoxicated patients. METHODS: PubMed, Scopus, Google Scholar, and clinicaltials.gov were searched for studies investigated the effects of oximes in the treatment of OP poisoning. Mortality, intermediate syndrome, intensive care unit (ICU) admission rate, and intubation rate were the key outcomes of interest. Data were searched in the time period of 1966 through December 2013. RESULTS: Ten studies (nine clinical trials and one historical cohort) that met our criteria were included in the analysis. Pooling of data showed that relative risk (RR) of need for intubation in OP poisoning for eight included trials comparing oximes to placebo was 1.27 with 95% CI= 0.73 to 2.23 (P= 0.4). RR of only one observational study was 1.57 (95% CI= 0.79 to 3.2, P>0.05). The summary of RR for mortality rate in 9 studies was 0.38 (95% CI= 0.65 to 2.97, P= 0.41) and for one observational study was 1.33 (95% CI= 0.54 to 3.29, P>0.05). The RR for ICU admission rate in OP poisoning for three trials comparing oximes to placebo was2.12 with 95% CI= 0.89 to 5.03 (P= 0.09). For only one observational study, RR was 0.81 (95% CI= 0.49 to 1.25, P>0.05). For intermediate syndrome, while the RR of only trial comparing oximes with placebo was 1.89 (95% CI= 1.27 to 2.91, P<0.05) while for only one observational study, it was 1.43 (95% CI= 0.7 to 2.96, P>0.05). CONCLUSIONS: According to these data, oximes beneficence in OP poisoning is unclear and if administered, great caution must be exercised because of increase in ICU admission rate and incidence of intermediate syndrome. Keywords: Organophosphorus, oxime, poisoning, meta-analysis