Objective: To examine whether horizontal head turns while seated or while walking, when instrumented with inertial sensors, were sensitive to the acute effects of concussion and whether horizontal head turns had utility for concussion management. Setting: Applied field setting, athletic training room. Participants: Twenty-four collegiate athletes with sports-related concussion and 25 healthy control athletes. Design: Case-control; longitudinal. Main Measures: Peak head angular velocity and peak head angle (range of motion) when performing head turns toward an auditory cue while seated or walking. Gait speed when walking with and without head turns. Results: Athletes with acute sports-related concussion turned their head slower than healthy control subjects initially (group β =-49.47; SE = 16.33; P =.003) and gradually recovered to healthy control levels within 10 days postconcussion (group × time β = 4.80; SE = 1.41; P <.001). Peak head velocity had fair diagnostic accuracy in differentiating subjects with acute concussion compared with controls (areas under the receiver operating characteristic curve [AUC] = 0.71-0.73). Peak head angle (P =.17) and gait speed (P =.64) were not different between groups and showed poor diagnostic utility (AUC = 0.57-0.62). Conclusion: Inertial sensors can improve traditional clinical assessments by quantifying subtle, nonobservable deficits in people following sports-related concussion.