The effect of the length of zinc oxide nanorods on their photoluminescence (PL) has been studied in the visible through UV spectral region. Hexagonally faceted columnar nanorods grown on (100) Si substrates have been shown to be aligned almost vertically. The chemistry of point defects in the nanorods depends on their position in the reactor during growth. The room-temperature PL spectrum of the nanorods shows narrow peaks due to stimulated free-exciton emission. The threshold optical pump power density for lasing in the longer ZnO nanorods is 8000 kW/cm(2), and the laser radiation is directed predominantly along their axis.