ABSTRACT OBJECTIVE To perform a cross-cultural adaptation of the Clear Communication Index instrument from the Centers for Disease Control and Prevention (CDC-CCI) from English to Brazilian Portuguese. METHODS This study comprised initial discussion about the conceptual equivalence of the instrument by a committee formed by experts on health education. We performed translations, synthesis of translations, back-translations, revision by the committee, and linguistic revision. Semantic equivalence was obtained by analyzing the referential and general meaning of each item by the committee, resulting in a pre-final version of the instrument. Subsequently, thirty professionals with health sciences degrees performed a pre-test. These professionals used the pre-final version of the instrument to assess a health education material. A questionnaire was applied to evaluate the acceptability of the instrument, the understanding of each of the 20 items, as well as the individual and professional variables. We analyzed the scores attributed to the health education material, the variables related to healthcare professionals, the proportions of the acceptability of the instrument, and the comprehension of each item. RESULTS After we obtained the conceptual equivalence of the instrument, the committee of experts, the instrument's main author, and the linguist produced the pre-final version using two translations, a synthesis of the translations, and two back-translations. A general equivalence was maintained in 15 of the 20 items (75%), four of the items were slightly altered (20%), and one item was very altered (5%). Nineteen items presented referential equivalence or near equivalence (95%). We then carried out with the pre-test, in which the professionals used the pre-final version. Two items in the domains of "risks" and "main message" were unclear and needed to be revised. CONCLUSION The process of cross-cultural adaptation of the Clear Communication Index provided an adapted version to the Brazilian Portuguese language.