The position of the image layer in simultaneous multilayer rotational panoramic radiography using films placed parallel in one cassette was calculated for curved and flat cassettes. Parallel films do not result in parallel layers. The use of a flat cassette results in minor shifts in layer position compared with a curved cassette. The position of the film required to produce parallel curved layers was calculated. Using curved cassettes, extraordinary modifications of the film position would be needed for the anterior region. The use of flat cassettes appears to be practically impossible. Routine use of this technique is therefore unlikely.