Alcohol-induced structural transformations of cetyltrimethylammonium bromide (CTAB) aggregates adsorbed on mica have been investigated using atomic force microscopy (AFM). A series of alcohols of different chain lengths was used to study the effect on surface aggregate structure. In CTAB solutions of fixed concentration, increasing amounts of alcohol spread the lateral spacing of the CTAB cylinders adsorbed on mice. At high alcohol concentrations, relative to the alcohol chain length, the surface aggregates changed from a cylindrical to a spherical structure. This structural transformation is explained by hydrophobic interactions between the alcohol and surfactant micelle.