This study was undertaken to definitively describe the internal anatomy of the median nerve. Thirty median nerves were dissected in the distal forearm and hand. Sixteen nerves were sectioned every 250 to 1000 microns along their length. Computer programs were developed in our laboratory to digitize and store the data. Analysis of our data has shown the following consistent findings: (1) the number of fascicles remains relatively constant over the centimeter lengths of the nerve; (2) over 75% of the sections contain zero to one fascicular branching; (3) fascicular groups destined for the same endpoint remain localized within the nerve for long distances; and (4) calculation of Wilks' lambda demonstrates a high degree of group fascicular regionality.