Powder neutron diffraction studies have been carried out on the fluorite-type Pb1-xAlxF2+x (0 less than or equal to x less than or equal to 0.12) solid solution. Three interstitial sites, F', F " and F''', were observed, in addition to the normal F-n sites of the fluorite structure at (1/4,1/4,1/4). Four types of fluoride sites, F-n, F', F " and F''', were identified with the four sublattices (F-n)(Pb), (F-ra)(Al), (F-i)(Pb) and (F-rd)(Al) suggested from F-19- and Al-27-NMR investigations. The clustering process proposed in Pb1-xAlxF2+x on the basis of NMR results is confirmed and the cluster characteristics are determined.