To compare the renal excursion detected by ultrasonography with the diaphragmatic excursion recorded by fluoroscopy in estimating the diaphragmatic function in patients with high cervical cord injury.Prospective, blinded comparative study.A rehabilitation hospital affiliated with a medical university.Fifteen consecutively admitted patients with high cervical cord injury.Not applicable.Chest radiographs, fluoroscopy of diaphragmatic motion, and ultrasonography of renal motion.Of the 15 patients, 2 were diagnosed with hemidiaphragm paralysis using fluoroscopy and renal ultrasonography. The average diaphragmatic excursion was 59 mm (range, 30-83 mm) in 28 nonparalyzed hemidiaphragms. The average renal excursion was 49 mm (range, 28-61 mm). The correlation coefficient for fluoroscopic hemidiaphragm excursion and ultrasonographic renal excursion was .853.Ultrasonographic renal excursion and fluoroscopic diaphragmatic excursion correlated highly. With the fluoroscopy results as the criterion standard, the diagnostic sensitivity and specificity were both 100% for renal sonography. With the advantages of convenience of use, no radiation exposure, and high reproducibility, renal ultrasonography is recommended as a first-line screening and long-term follow-up tool for assessment of diaphragmatic function.