Naphthalene, anthracene and 2,3-benzanthracene were incorporated into the pores of the crystal structure of the zeolite Y. The localisation of the guest molecules was performed by powder diffraction, Fourier analysis and Rietveld refinement. All guests were situated in similar positions in the supercage in front of the sodium cation at position II. However systematic differences in the precise adsorption position of these different guests were observed and can be correlated with the size of the guest molecules.