en Design and Psychometric Evaluation of a Sexual Health Knowledge Scale for University Students Aims: This study aimed to design and evaluate the validity and reliability of a questionnaire regarding sexually transmitted infections and HIV/AIDS knowledge among undergraduate university students in Iran. Instrument & Methods: This research was conducted in 2018 among university students in Tehran, Iran. The questionnaire was designed to measure knowledge of sexually transmitted infections and HIV/AIDS by reviewing the relevant literature and consulting expert panels for item production in the initial step. The next step was to assess the instrument’s face and content validity. The internal consistency (Cronbach’s α) and interclass correlation coefficient were used to evaluate the reliability of the questionnaire. Findings: The face validity of the developed scale was considered appropriate, with an impact score greater than 1.5. The content validity, measured through the content validity index and content validity ratio for knowledge items related to sexually transmitted infections and HIV/AIDS, varied from 0.80 to 1. The Cronbach’s α was 0.88 for sexually transmitted infection knowledge items and 0.86 for HIV/AIDS knowledge items. The interclass correlation coefficient values for the sexually transmitted infection and HIV/AIDS knowledge items were 0.86 and 0.85, respectively, indicating satisfactory reliability outcomes. Conclusion: The questionnaire on sexually transmitted infections and HIV/AIDS knowledge for Iranian young adults demonstrates satisfactory validity and reliability. Surveys and Questionnaires,Acquired Immunodeficiency Syndrome,Sexually Transmitted Infections (STIs),HIV,Young Adults, 171 177 http://daneshafarand.org/browse.php?a_code=A-10-11568-4&slc_lang=en&sid=4