Sexually transmitted diseases (STDs) continue to remain a public health concern in the United States, especially among young people. Levels of knowledge with regard to STDs have been investigated in prior research; however, these investigations have been limited primarily to older adolescents and young adults. Grounded in the social cognitive and subjective culture theories, this quantitative, cross-sectional study assessed STD knowledge (other than HIV/AIDS) among 7th grade students attending a public middle school in the United States. Demographic differences (age, gender, and ethnicity) in STD knowledge were examined to determine if these demographic variables predict STD knowledge scores and if the Sexually Transmitted Disease Knowledge Questionnaire (STD-KQ) is a valid and reliable instrument among this study population. Chi-square analysis demonstrated that STD knowledge scores significantly differed by age only: Twelve-year-olds had higher STD scores than did 13-year-olds, contrary to research in older adolescents, which may be the result of confounding factors that warrant further investigation. Multiple regression analysis showed that age, gender, and ethnicity were not associated with STD knowledge scores. The STD-KQ was found to have face validity as well as high consistency and reliability among all questions related to STDs other than HIV/AIDS using Crohnbach's alpha. Content validity for individual STD-KQ items was shown using Lawshe's content validity ratio and subject matter experts. Results of the study support positive social change and highlight the need for earlier STD education, other than HIV/AIDS, with middle school children and the need to examine other factors that may impact STD knowledge within this age group.