The distribution of organic guest molecules within NaY zeolites has been examined utilizing aromatic molecules as photophysical probes. The distribution of guests within zeolites has been shown to be nonuniform. Three parameters-guest occupancy, families of sites, and distribution of sites within a family-are defined, and the results are analyzed on their basis. Coadsorbed molecules such as water and organic solvents influence significantly the guest distribution within zeolites.