Since Major League Baseball (MLB) expanded to its current size of 30 teams in 1998, a comprehensive and longitudinal study of injury trends has not been performed. The purpose of this work is to report the epidemiology of injuries in MLB over that time utilizing disabled list (DL) data. Additionally, we sought to determine the financial impact of these injuries for MLB teams. During this analysis, we focused special attention on injuries of the medial ulnar collateral ligament (MUCL) and conducted a comprehensive review of all MUCL reconstructions ever performed on MLB players. Over the study period, there were a total of 8357 DL designations (mean of 464 annually). Players lost a total of 460,432 days (25,186 days annually) due to injury. Both the number of DL assignments and number of DL days increased from year to year (P < .001 and P = .003, respectively). Average length of DL assignments remained steady over time at 55.1 days (P = .647). Although shoulder injuries decreased (P = .023), this was met with a reciprocal increase in elbow injuries (P = .015). The average annual cost of designating players to the DL was $423,267,634 and a total of $7,618,817,407 was spent over the entire 18 seasons. Regarding MUCL injuries, a total of 400 MUCL reconstructions were performed in MLB players between 1974 and 2015, and the mean time to return to MLB competition was 17.1 months. The annual incidence of MUCL reconstructions increased dramatically from year to year (P < .001) and nearly one-third (n = 131, 32.8%) of all procedures performed over the 42-year period occurred in the last 5 years (2011 to 2015). In summary, overall injury rates and DL assignments continue to rise. Although shoulder injuries are declining, this improvement is countered by increasing elbow injuries, and these injuries continue to represent a significant source of lost revenue.