Multilayer films of preformed polyimide molecules have been obtained for the first time by the Langmuir-Blodgett technique. The pressure-area isotherm shows that the polyimide monolayers are strongly dependent on compression rate. The zero-pressure area per repeat unit is about 1.7 nm(2) when the film is compressed at 100 cm(2)/min. This value is higher than that expected (1.2 nm(2)) for a closely packed structure. Multilayers have been investigated with X-ray reflectometry. The thickness of a bilayer film is about 4.05 nm, which is between the average bilayer thickness of a interdigitated multilayer film and that of a bilayer film containing closely packed backbones and fully extended alkyl side chains. The multilayer films do not display a distinctively periodic structure. When the films are annealed for a few hours at 180 degrees C, the structure relaxes somewhat and thickness decreases slightly.