In the classical approach of determining the stresses and displacements due to a centrifugal force in rotating disks, the inertia force considered does not include the radial displacement thus yielding stable solutions. Inclusion of the displacement in the centrifugal force results in instability at certain rotational speeds. The present study addresses the problem of instability in rotating polar-orthotropic disks. Following a brief outline of the classical analysis, the stress redistribution solutions are presented. The solutions are obtained in terms of non-dimensional parameters. The parameter defined as the ratio of circumferential stiffness to radial stiffness has been found to have the most considerable effect on the critical rotational speed. Various cases are considered, and the corresponding critical rotational parameters are presented in tables, The comparison of stresses obtained from the classical approach with the redistributed stresses is displayed graphically. (C) 2000 Elsevier Science Ltd. All rights reserved.