The evolution equation is obtained for the state of polarization of partially polarized radiation propagating in a medium that is nonuniform and fully anisotropic, i.e., that presents both linear and circular birefringence as well as dichroism. The treatment covers the general case in which the characteristic polarizations are not necessarily orthogonal, such as occurs for propagation in a magnetized, dissipative plasma. The differential Mueller matrix that appears in the evolution equation is obtained explicitly for two particular cases. The resulting formalism is convenient for numerical integration.