Some information about the aggregation in aromatic fluorocarbon-aromatic hydrocarbon systems was obtained on the basis of the Kirkwood-Buff theory of solution. The Kirkwood-Buff integrals and the excess (or deficit) number of molecules aggregated around a central one were calculated for the following systems: hexafluorobenzene-benzene, hexafluorobenzene-toluene, hexafluorobenzene-cyclohexane, benzene-toluene, and benzene-cyclohexane. It was found that the composition dependence of the excess (or deficit) number of molecules aggregated around a central one for the systems hexafluorobenzene-benzene and hexafluorobenzene-toluene has a nontypical character since it changes sign for a mole fraction of about 0.4 for the former and 0.2 for the latter. It was found that such compositions correspond to extrema ill the activity coefficients and inflection points in the excess Gibbs energy. The excess (or deficit) number of molecules aggregated around a central one in the systems investigated allowed us to conclude that in the mixtures hexafluorobenzene-benzene and hexafluorobenzene-toluene there are some like (enriched in the same component as the central one) aggregates for mole fractions of hexafluorobenzene smaller than 0.4 and 0.2, respectively, and some unlike aggregates for larger values of mole fraction of hexafluorobenzene. The change of aggregation from like to unlike as well as its moderate temperature dependence suggest that the interactions involved are not too strong. In addition, because the radius of the correlation volume (the volume affected by the presence of a molecule) is relatively large (similar to 10 Angstrom), the interactions are relatively long range. In the other mixtures investigated, only like aggregates were formed and for the mixture hexafluorobenzene-cyclohexane relatively large like aggregation of hexafluorobenzene was found.