The solution of the system of equations of plane simple waves in a Prandtl-Reuss isotropically work-hardening medium is reduced in general (without any assumptions on the form of the work-hardening function and the state in front of the simple wave) to the investigation of an ordinary differential equation of the first order. In the special case of linear work-hardening, and also without work-hardening, the solution of the system of equations for plane simple waves is obtained in quadratures. The problem of an oblique shock on a prestressed half-space with arbitrary uniform constant stresses is solved for a linearly work-hardening medium.