Background The System Usability Scale (SUS) is a common metric used to assess the usability of a system, and it was initially developed in English. The implementation of electronic systems for clinical counseling (eHealth and mobile health) is increasing worldwide. Therefore, tools are needed to evaluate these applications in the languages and regional contexts in which the electronic tools are developed. Objective This study aims to translate, culturally adapt, and validate the original English version of the SUS into a Spanish version. Methods The translation process included forward and backward translation. Forward translations were made by 2 native Spanish speakers who spoke English as their second language, and a backward translation was made by a native English speaker. The Spanish SUS questionnaire was validated by 10 experts in mobile app development. The face validity of the questionnaire was tested with 10 mobile phone users, and the reliability testing was conducted among 88 electronic application users. Results The content validity index of the new Spanish SUS was good, as indicated by a rating of 0.92 for the relevance of the items. The questionnaire was easy to understand, based on a face validity index of 0.94. The Cronbach α was .812 (95% CI 0.748-0.866; P<.001). Conclusions The new Spanish SUS questionnaire is a valid and reliable tool to assess the usability of electronic tools among Spanish-speaking users.

BACKGROUND The mHealth concept encompasses the use of mobile devices for clinical counseling. The System Usability Scale (SUS) is a common metric used to assess the usability of a system. The SUS was initially developed in English, and it would need to be updated and adapted to languages and regional contexts in which the electronic tools are developed. OBJECTIVE The objective of this study is to translate, culturally, adapt, and validate the original English version of the SUS into a new Spanish version. METHODS The translation process included forward and backward translation, forward translations was made by two native Spanish speakers, who spoke English as their second language, and backward translation was made by an English native speaker. The Spanish SUS questionnaire was validated by 10 experts in mobile app development. The face validity of the questionnaire was tested on 10 mobile phone users, and finally, the reliability testing was probed in 88 electronic app users. RESULTS The content validity index of the new Spanish SUS was good based on the rating of the relevance of items of 0.92. The questionnaire was easy to understand based on the face validity index of 0.94. According to Cronbach’s alpha test 0.81 IC95% (0.74 – 0.86), the translated scale is s a reliable tool for the assessment of the usability of electronic tools. CONCLUSIONS The new Spanish SUS questionnaire is a valid and reliable tool to assess the usability of electronic tools for Spanish users,