Background: As the incidence of ulnar collateral ligament (UCL) surgery continues to rise rapidly, an update on the current prevalence and demographics in professional baseball players is warranted. Hypothesis: The prevalence of UCL reconstruction in Major League Baseball (MLB) and Minor League Baseball (MiLB) players will be higher than that previously reported, and the increase in prevalence will be most notable in MiLB pitchers. Study Design: Cross-sectional study; Level of evidence, 3. Methods: During the 2018 baseball season, an online questionnaire regarding a history of UCL surgery was distributed to the certified athletic trainers of all 30 MLB organizations. These trainers then administered the survey to all players within their organizations, including MLB, MiLB (AAA, AA, High A, Low A, High Rookie, Low Rookie), and Dominican Summer League (DSL) players. Demographics were compared between MLB, MiLB, and DSL players. Results of this 2018 survey were compared with previously published data from the 2012 season to assess the change over time. Results: There were 6135 professional baseball players who completed the survey (66% response rate). The prevalence of UCL reconstruction in all MLB and MiLB players was 13% (637/4928), while the prevalence in DSL players was 2% (20/1207) ( P < .001). The prevalence in all MLB and MiLB players (13%) and pitchers (20%) both increased significantly from 2012 ( P < .001). MLB pitchers reported a higher prevalence of UCL reconstruction than did MiLB pitchers (26% vs 19%, respectively; P < .001). In 2018, the prevalence of UCL reconstruction has increased significantly in MiLB pitchers (19% vs 15%, respectively; P < .001) and pitchers aged 21 to 30 years (22% vs 17%, respectively; P < .001) compared with 2012. Additionally, United States–born pitchers were more likely to have undergone UCL reconstruction compared with Latin America–born pitchers (23% vs 13%, respectively; P < .001). Conclusion: The prevalence of UCL reconstruction has increased significantly in professional baseball players over the past 6 years from 10% to 13%. Ultimately, the prevalence of UCL reconstruction has increased most significantly since 2012 in MiLB pitchers, pitchers aged 21 to 30 years, and pitchers born in the United States.