The synthetic method has been incorporated into a technique (called the Sn synthetic method) for accelerating the iterative solution of two-dimensional discrete ordinate equations. For model problems, convergence of the method is established and bounds on the rate of convergence obtained. The analytical results coupled with numerical results for more general problems indicate that the Sn synthetic acceleration technique is extremely effective for problems containing large regions where the ratio of the scattering to total cross section is close to unity.