PURPOSE: Tibial stress fracture is a common overuse running injury resulting from repetitive mechanical loading. This research project aimed to determine whether runners with a history of tibial stress fracture (TSF) differ in tibial bone geometry, tibial bone mass, and ground reaction force (GRF) parameters during running from those who have never sustained a stress fracture (NSF). METHODS: Forty-six male running athletes (23 TSF; 23 NSF) ranging in age from 18 to 42 yr were recruited for this cross-sectional study. A force platform was used to measure selected GRF parameters (peak and time to peak for vertical impact force, vertical active force, and horizontal braking force) during running at 4.0 m x s(-1). Tibial bone geometry (cross-sectional dimensions and area) was calculated from a computerized tomography (CT) scan at the junction of the middle and distal thirds. Dual energy x-ray absorptiometry (DXA) provided measurements of tibial bone area, bone mineral content (BMC), and bone mineral density (BMD). RESULTS: The TSF group had significantly smaller tibial cross-sectional area (P = 0.02) and DXA tibial bone area (P = 0.02), after adjusting for height and weight, than the NSF group. There were no significant differences between groups for GRF, tibial BMC, or tibial BMD. CONCLUSION: These findings support the contention that bone geometry plays a role in stress fracture development and that male athletes with smaller bones in relation to body size are at greater risk for this bony injury.