OBJECTIVES: The translation of PRO measures requires a rigorous procedure, including dual forward translations, reconciliation, back translation and review, and debriefing interviews. The relevance of including blinded back translations has been widely discussed; however, there has been little discussion around back translation methods. This research aims to gauge the importance of having two back translations versus only one. METHODS: Past translation and linguistic validation projects employing the procedures outlined above were reviewed to compare the methodology of using one back translation versus two. RESULTS: In the dual-back projects, numerous instances were found in which only one back translator detected an issue. For example: 1. Simple mistranslations can be revealed by one translator but not another; e.g. ‘activities at home’ was back translated verbatim by one back translator but as ‘household activities’ by another, revealing that the translated term was too narrow and related only to chores; 2. Similarly, contextual mistranslations may become apparent in dual back translations. In one ePRO script, ‘enter training module’ meant to click through to the next page. One back translator wrote ‘enter’, while ‘insert’ in the second translation highlighted that the wrong term had been used in this context; 3. Dual translations are also useful for elucidating nuances in meaning. In Danish, the phrase ‘bad tempered’ became ‘lose my temper’ in one back translation, allowing the lead translator to alter the ambiguous translation; 4. Dual meanings in the target language may also be highlighted, for example in Gujarati ‘hospitalisations’ was correctly back translated by one translator, but the other translated it as ‘clinic’, showing an ambiguity in the translation. CONCLUSIONS: The high proportion of issues highlighted by only one back translator, show the importance of using two blinded back translators in the translation of PRO measures.