The purpose of this study is to determine the range of maximal diaphragmatic crural thickness during different phases of respiration and to correlate crural thickness with age and gender. Prospective evaluation of computed tomographic (CT) scans of 200 patients without juxtacrural abnormalities was performed. Maximal short-axis crural thickness measurements were determined in all patients. Measurements were obtained at full inspiration during chest CT (n = 60), full expiration during abdominal CT (n = 89), and unknown phase of respiration during dynamic CT scans (n = 51). Maximal crural thickness measurements were analyzed by side, age, and gender. The right crus was thicker than the left crus in 91% of patients. The range of maximal crural thickness remained fairly constant from the second to the eighth decades of life. The range of maximal crural thickness was 1.8-18.8 mm in men and 1.8-21.1 mm in women. Maximal crural thickness does not significantly vary with age and gender for specific phase of respiration.