Pairs of gold nanodisks 40 or 70 nm in diameter were fabricated in silica by electron-beam lithography. On irradiation by 110 MeV Br(10+) ions, the nanodisks elongated to form nanorods; elongation occurred in the direction of propagation of the ions. The aspect ratios of the Au nanorods increased with increasing ion-flux density or fluence and with decreasing diameter of the nanodisks. The elongation mechanism can be explained in terms of a thermal spike model.