Results on scattering, off-center coupling, and other losses that influence the shape of a beam delivered by flexible hollow waveguides are presented. The conditions for the beam shape to be near to that of the source are found. A theoretical model for the radiation propagation through the hollow waveguides and the conditions for change in the beam shape are calculated. Good agreement between the theoretical and experimental results was obtained. © 2000 Society of Photo-Optical Instrumentation Engineers.