The aim of this study was to translate into Persian and validate a questionnaire on knowledge about sexually transmitted diseases published by Jaworski and Carey in 2007. The questionnaire was forward-translated by two bilingual translators, and both translations were discussed by an expert team. The questionnaire was then back-translated by two other bilingual translators and discussed with both of them. Two sex-segregated focus group discussions were held with 21 health care providers to evaluate the comprehensibility of the questions. The final Persian version of the questionnaire was administered to 130 randomly selected health care providers in Rasht in 2014 to assess internal consistency and convergent and discriminant validity. The Cronbach’s alpha coefficients were 0.84 for the overall questionnaire, 0.75 for the cause/cure subscale and 0.74 for the general knowledge subscale. The correlation between an item and its subscale was significantly higher than its correlation with other subscales. The Persian version of the questionnaire is highly valid and reliable and can be used as a standard instrument for evaluating knowledge about sexually transmitted infections in the Islamic Republic of Iran.