Background With increasing rates of sexually transmitted infections in the United States, there is a critical need to educate health professionals on the prevention, diagnosis, and treatment of sexually transmitted infections. The National Sexually Transmitted Disease Curriculum (NSTDC, https://www.std.uw.edu) is a free, online curriculum, funded by the Centers for Disease Control and Prevention. The purpose of this article is to evaluate the reach, utilization, and engagement of users with the curriculum. Methods Data on NSTDC utilization was collected for 24 months after the February 1, 2017 launch. For all users, Google Analytics was used to determine total number of users, geographic location, age and sex, and average session duration. For registered users, additional data analysis included work-role, demographics, and completion of self-study modules, check-on-learning questions, and question banks. User satisfaction was measured on a 5-point Likert scale. Results During the evaluation period, 136,270 individual users accessed the NSTDC, including 24,652 registered users. Among all registered users, 10,660 (43.2%) were registered nurses, 2810 (11.4%) physicians, 4942 (20.1%) Advanced Practice Nurses and Physician Assistants, and 6213 (25.2%) nonclinicians. Among registered users, 18,533 (75.2%) completed at least 1 module, 7898 (32.0%) completed all 7 modules, and 19,804 (80.4%) answered optional check-on-learning questions. Median satisfaction with the content was (5) very satisfied (interquartile range, 4-5). Conclusions The NSTDC is a free, guideline-based, online curriculum with novel dual functionality that has achieved extensive reach with a broad array of health professionals who engage deeply with the material. The wide usage of NSTDC demonstrates the need for high-quality, unbiased, free content in user-focused formats.