Myelinated axons in the human lateral corticospinal tract (LCST) at the C6 and L4 levels were examined on 16 male cadavers, with age ranging from 41 to 88 years. The average area of axons in the LCST was measured using a microscopic image-analyzing system. Our data show that the average area of axons at the C6 and L4 levels decreased with age. We also noticed that the average area of axons was larger at the C6 level than at the L4 level in all cases. This decrease may be related to a parallel decrease of conduction velocity in the LCST during the ageing process.