Our purpose was to assess the impact of a curriculum designed to improve third-year medical students' knowledge of sexually transmitted diseases, measured by sexually transmitted disease-related items from the National Board of Medical Examiners subject examination and by a locally developed sexually transmitted disease test. All students (n = 108) were exposed to a new sexually transmitted disease curriculum: a 2-hour laboratory module, lectures, syllabus, and locally developed pretest/posttest with review of the test prior to taking the National Board of Medical Examiners subject examination. Students were randomized to a attend sexually transmitted disease clinic (n = 47) versus no sexually transmitted disease clinic (n = 61). Students performed equal to or better than the national average on 85% of the National Board of Medical Examiners sexually transmitted disease-related items after curriculum institution, compared with 56% of the test items prior (P <. 001). Magnitude of improvement was dependent on clerkship timing, with greater improvement in students taking the obstetrics-gynecology clerkship earlier in the third year. Mean postcurriculum test scores of sexually transmitted disease improved significantly (P <. 001), independent of clinic site and clerkship timing. The curriculum for sexually transmitted disease produced significant improvement in third-year medical students' knowledge of sexually transmitted disease. This might have an impact on future prevention and control of sexually transmitted diseases in communities in which these students practice. © 2004 Elsevier Inc. All rights reserved.