The purposes of this study were to visualize the human median nerve on diffusion tensor imaging and to determine the normal fractional anisotropy (FA) value and apparent diffusion coefficient (ADC) of the normal median nerve. The wrists of 20 healthy volunteers and of two patients with carpel tunnel syndrome were examined with a 3-T MRI system with a standard eight-channel sensitivity-encoding head coil. Diffusion tensor imaging was performed with a spin-echo echo-planar sequence. A T1-weighted sequence was performed for anatomic reference. After tractography, the FA value and ADC of the whole nerve were calculated automatically. Manual focal measurements also were obtained at the levels of the flexor retinaculum, wrist, and forearm. We visualized the median nerve with MR diffusion tensor tractography and followed the nerve for approximately 77.5 mm. We found the normative diffusion values of the median nerve were an FA of 0.709 +/- 0.046 (SD) and an ADC of 1.016 +/- 0.129 x 10(-3) mm2/s. There was a statistically significant difference between the FA values obtained at the level of the flexor retinaculum and the values obtained from the other parts of the median nerve (p < 0.0001). We found a decrease in FA value (p < 0.01) and an increase in ADC (p < 0.05) with advancing age. The normative diffusion values of the human median nerve can be used as a reference in evaluation, diagnosis, and follow-up of entrapment, trauma, and regeneration of the median nerve.