Adsorption of the chiral hydrocarbon heptahelicene on Cu(111) has been investigated by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at cryogenic temperatures. The pure enantiomers form extended chiral structures which are mirror images of each other and mirror domains are observed after adsorption of the racemic mixture. Although periodicity and orientation of the adsorbate lattices with respect to the substrate lattice are almost identical, as concluded from LEED, STM reveals different local structures for racemic mixture and pure enantiomers. This is explained by quasi-hexagonal two-dimensional packing in all structures but different relative azimuthal orientations of the molecules within the adsorbate lattice. [DOI: 10.1380/ejssnt.2004.136]