A boundary condition for nonlinear quasiplane wave propagation in a wide tube is given taking into account Stokes boundary layer effects. Wave motion is described by the Khokhlov–Zabolotskaya–Kusnetzov equation. An asymptotic scheme for the solution is based on matching acoustic and boundary layer expansions. In the case of plane motion, the model is reduced to the generalized Burgers equation obtained previously by Blackstock. Numerical results and comparison with experiment are demonstrated. The latter shows that there is good agreement in general, although some specific details are still unclear.