Objectives: Ulnar collateral ligament reconstruction (UCLR) is a successful procedure in professional baseball players. It is unclear if hamstring tendon harvest side for UCLR alters a player’s risk of subsequent hamstring injuries. The purpose of this study was to compare, performance, return to sport (RTS) rate, and injury rates between professional baseball players with a history of UCLR using an ipsilateral (drive leg) hamstring autograft to those with UCLR using contralateral (landing leg) hamstring autograft. The authors’ hypothesized that players with prior UCLR using ipsilateral (drive leg) hamstring autograft will have the same RTS rate and performance upon RTS, but higher number of subsequent lower extremity injuries than those using contralateral (landing leg) hamstring autograft. Methods: All players between 2010-2015 who underwent UCLR using hamstring autograft were included. Surgical details of their procedure were recorded using operative reports. Players with a hamstring UCLR were compared within group to compare grafts taken from the drive leg vs. landing leg. Results: Overall, 191 players underwent UCLR using hamstring autograft (58 [30%] landing/contralateral and 133 [70%] ipsilateral/drive leg). The docking technique was more common in the contralateral/landing leg group while the figure-of-8 technique was more common in the ipsilateral/drive leg group (p>0.001). More patients in the ipsilateral/drive leg group underwent concomitant treatment of the ulnar nerve than the contralateral/landing leg group (p<0.001). No difference existed in return to sport (RTS) rates, or timing of RTS between groups. No differences in subsequent ipsilateral or contralateral hamstring injuries between players who underwent UCLR using hamstring from the ipsilateral/drive leg or contralateral/landing leg was seen (p=1.000; p=0.460 respectively). No difference in overall upper or lower extremity injury rates existed between groups. Conclusion: No difference in RTS rate, performance upon RTS, or subsequent hamstring, lower extremity, or upper extremity injury rates existed between players who underwent UCLR using hamstring autograft from the ipsilateral/drive or contralateral/landing leg.