IntroductionTo produce robust evidence RCTs need to be rigorously conducted as poorly performed studies introduce bias and can mislead clinicians and policy makers. Poor allocation concealment has the largest single impact on bias in RCTs than other methodological aspects. Envelopes are frequently used as a method of allocation concealment and can be associated with increased risk of bias. This paper aims to review envelope use in RCTs published in 2017?2018 and create a guide as a reference for researchers when planning and publishing RCTs when using envelopes as an allocation concealment method.MethodsRCTs that used envelopes as a form of allocation concealment that were published in BMJ, JAMA, NEJM and The Lancet in 2017 and 2018 were identified and methodological data on their envelope use extracted and authors were contacted to ascertain reasons for using envelopes in their research.Results338 RCTs were identified that were published in 2017 and 2018. 8% (n?=?29) of the RCTs published used envelopes as an allocation concealment method. 24.1% (n?=?7) of studies reported envelope studies robustly with all required methodological information stated to enable an assessment of quality. Budget was the most frequent reason given for envelope use (41.7%).DiscussionOnly 24% of published RCTs, that used envelopes, contained robust methodological information to enable the reader to judge whether the randomisation and allocation concealment method was adequate.ConclusionRCTs are not reporting envelope use well. RCTs using envelopes should be designed and reported clearly ensuring all necessary methodological information is included.