The structural characteristics of perhydrogenated carbon and boron nitride nanotubes are determined by means of quantum chemical calculations. Two families of nanotubes ore systematically studied for both carbon and boron nitride, the nanotubes being derived from the perhydrogenated (110) and (111) sheets of diamond and cubic boron nitride. Single-walled perhydrogenated carbon nanotubes prefer structures analogous to the (111) sheet. In clear contrast, the single-walled perhydrogenated boron nitride nanotubes prefer structures analogous to the (110) sheet. The significantly different structural characteristics are due to the polarization of hydrogen atoms in the perhydrogenated boron nitride nanotubes. The presence of attractive electrostatic H-H interactions leads to a strong preference for multilayering of the boron nitride sheets and nanotubes. The results ore expected to provide new insights into the structural characteristics of main-group binary hydrides.