The objectives of this study were to (1) use kinetics from motion analysis and inverse dynamics to calculate the stress experienced by the ulnar collateral ligament (UCL) during a typical pitch cycle, (2) compare calculated maximum UCL pitching stresses to failure properties, and (3) investigate correlations between UCL stress with anthropometric and pitching biomechanical parameters. Prior motion analysis experiments of eighteen 10- to 11- year-old baseball pitchers throwing 10 fastballs were analyzed. Maximum internal elbow varus torques were calculated using inverse dynamics methods during a typical pitch cycle. Calculations used axial loading stress equations and maximum internal elbow varus torques to quantify the maximum UCL pitching stresses. UCL ultimate stresses and number of cycles to failure were calculated from prior studies with a scaling procedure to estimate youth participant values. The calculated maximum UCL pitching stresses were then compared to the estimated ultimate stresses using a paired t-test. The first major result of this study was that the maximum UCL pitching stresses were 33.83 MPa lower, on average, than the estimated ultimate stresses (p < 0.001). A second major result of this study was the estimated average number of cycles to failure of the UCL were 80,000+ higher, on average, than the maximum season (p < 0.001) and annual (p < 0.001) pitch counts. A third major result of this study was maximum UCL pitching stresses were significantly and positively correlated with pitch speeds, maximum shoulder external rotation torque, and maximum elbow varus torque. These results suggest 10- to 11- year-old pitchers are not likely to experience a UCL injury. The findings of this study are supported by clinical observations of elbow injuries in youth pitchers occurring primarily in other tissues.