Following the synthesis of aligned single-wall carbon nanotubes in the channels of AlPO-5 zeolite single crystals, we present the first X-ray diffraction and diffuse scattering results. They can be analyzed in terms of a partial filling of the zeolite channels by nanotubes with diameter around 4 angstroms. The possible selection of only one type of nanotube during the synthesis, due to the constraints imposed by the zeolite host, is discussed.