Abstract Room temperature grown Na films on Cu(1 1 1) were investigated with low temperature scanning tunneling microscopy (STM) at coverages Θ=0.3 to 1.1 (ML) (monolayer, ML). A p(3×3) reconstruction with four atoms per unit cell at full ML coverage is observed in accord with previous low energy electron diffraction data. For coverages below Θ=1 ML, a structure model is proposed. We find that an analysis of the electronic structure of the Na overlayer state provides complementary information for the characterization of the films. For the second ML Na film, island growth is observed. From an analysis of the STM data of the second ML Na film, a structure model is developed.