A method of generating a class of exact solutions for three‐dimensional boundary layer flows is presented. These are solutions to the initial value problem for steady, incompressible flow. In one type the history upstream of the initial plane is known; in a second type this history is not known. A power law pressure gradient exists in the streamwise direction but the cross flow decays under zero cross pressure gradient. The essential restriction for obtaining exact solutions is that all quantities not depend on the cross stream coordinate. The solutions are obtained as expansions in terms of eigenfunctions. The cross flow and the streamwise vorticity decay algebraically with powers that depend on the pressure gradient and eigenvalues. An S‐shaped initial profile has a decay rate approximately twice as great as a C‐shaped initial profile; the former requires a few hundred boundary thicknesses to decay appreciably. The decay rate is only mildly dependent on the streamwise pressure gradient. These results of physical interest in three‐dimensional boundary layer flows are obtained without extensive numerical calculations.