The distribution of aluminum in MCM-22 zeolite has been studied by Al-27 solid-state nuclear magnetic resonance. Three different aluminum species in tetrahedral position were observed. Surface selective dealumination with oxalic acid causes the disappearance of one of the NMR signals at 50.5 ppm. The corresponding species have been attributed to aluminum atoms located in the 12-T large cavities located on the external surface of the zeolite crystals.