Prior studies have revealed magnetic resonance imaging (MRI) evidence of elbow pathology in single-season evaluation of competitive youth baseball players. The natural history of these findings and risk factors for progression have not been reported.To characterize the natural history of bilateral elbow MRI findings in a 3-year longitudinal study and to correlate abnormalities with prior MRI findings, throwing history, playing status, and physical examination.Cohort study; Level of evidence, 2.A prospective study of Little League players aged 12 to 15 years was performed. All players had preseason and postseason bilateral elbow MRI performed 3 years before this study. Players underwent repeat bilateral elbow MRI, physical examination, and detailed assessment of throwing history, playing status, and arm pain. Imaging was read by a blinded musculoskeletal radiologist and compared with prior MR images to assess for progression or resolution of previously identified pathology.All 26 players who participated in the previous single-season study returned for a 3-year assessment. At the completion of the study, 15 players (58%) had dominant arm MRI pathology. Eighty percent (12/15 players) of MRI findings were new or progressive lesions. Players with postseason MRI pathology at the beginning of the study were more likely to have MRI pathology at the 3-year follow-up than players with previously normal postseason MRI ( < .05), although 6 of the 14 players (43%) with previously normal MRI developed new pathology. Year-round play was a significant predictor of tenderness to elbow palpation ( = .027) and positive MRI findings at 3 years ( = .047). At the 3-year follow-up, 7 players (27%) reported having throwing elbow pain and 3 had required casting. Additionally, differences were noted in the dominant arm's internal and external rotation in those that continued to play baseball ( < .05).Dominant elbow MRI abnormalities are common in competitive Little League Baseball players. Year-round play imparts significant risk for progression of MRI pathology and physical examination abnormalities.