Sixty patients with simple diaphyseal tibial fractures were randomized to receive fracture fixation with a small diameter (n=30) or a large diameter interlocking reamed intramedullary nail (n=30). The outcomes of interest included radiological exposure, operative time, time to union, the incidence of anterior knee pain, return to full knee range of motion, and post-operative complications. The small-diameter nail demonstrated longer time to union (15.2 weeks vs. 12.8 weeks, p=0.003), but with significantly less radiological exposure and operative time. However, clinical and radiological outcomes (incidence of anterior knee pain, return to full range of motion, incidence of implant failure, non-union) were comparable between the two groups. Small-diameter nails may offer comparable outcomes to long-diameter nails for the treatment of simple tibial shaft fractures.