This paper presents a method for the dynamic analysis of initially tensioned orthotropic thin-walled cylindrical tubes conveying steady #uid #ow, based on Sanders' non-linear theory of thin shells and the classical potential #ow theory. The method is relatively straightforward, using a hydrodynamic pressure formulation derived from the velocity potential, a dynamic coupling condition at the #uid}structure interface and two-noded frustum elements to assess the dynamic behaviour of these tube/#uid systems accurately. A non-linear strain}displacement relationship is also deployed to derive the geometric sti!ness matrix due to the initial stresses and hydrostatic pressures. The equations of motion for the tube and #uid are solved by a "nite element method, and this is validated by comparing the natural frequencies obtained with other published results. The in#uence of material properties, fluid flow velocities and initial axial tensions on the natural frequencies is then illustrated and discussed.