WHAT IS ALREADY KNOWN ON THIS TOPIC: Previous out-of-hospital studies indicate that selective spinal immobilization may miss patients with cervical injury. WHAT QUESTION THIS STUDY ADDRESSED: Can paramedics apply the Canadian C-Spine Rule in alert, stable, cooperative, blunt-trauma patients to reserve spinal immobilization for high-risk patients while avoiding immobilization for low-risk patients? WHAT THIS STUDY ADDS TO OUR KNOWLEDGE: In this 1,949-patient cohort, paramedics achieved 100% sensitivity and 38% specificity for important cervical fractures. HOW THIS MIGHT CHANGE CLINICAL PRACTICE: Use of the Canadian C-spine Rule by paramedics may safely avoid unnecessary spinal immobilization.