The effect of viscous heating on the linear stability of torsional flow of a viscoelastic fluid is analyzed. We consider an Oldroyd-B fluid subjected to a steady shearing motion in a cone-plate system with small gap. Previous experimental and analytical results show that in the isothermal case the flow is unstable to short wavelength disturbances for values of the Deborah number greater than some critical value. In this paper we show that viscous heating, which is characterized by a radially averaged Nahme number, (Na) over tilde, has a stabilizing effect on both long wave and short wave disturbances. This is in qualitative agreement with experimental results of Rothstein and McKinley.