The paper deals with reradiation from the interior of cylindrical conducting structures of finite length and arbitrary termination. Expressions are developed for far fields at points in the principal plane. For rectangular cross-sections this plane is one containing a broad side of the structure, whereas for circular cross-sections it is a plane containing the longitudinal axis of the structure. Incident plane waves having the propagation vector parallel to the principal plane and polarised either vertically or horizontally with respect to the principal plane are considered. The method of solution involves use of normal-mode techniques in conjunction with the Stratton-Chu integral.Comparisons of computer-calculated theoretical data and measured data were made for illumination of rectangular and circular structures. The theoretical and experimental data, which were for zero bistatic angle and short-circuit terminations of the structures, show remarkably good agreement. For aspect angles of less than about 60°, the return from the interior is dominant, while for larger aspect angles the return from the outer surface masks the interior return. The theory is also valid for nonzero bistatic angles.