An approximate method is presented for calculating the unsteady quasi-two-dimensional incompressible laminar boundary layer. The velocity profiles are assumed to be given by one-parameter families of curves, the parameter being essentially the non-dimensional shearing stress at the wall. The profile parameter and the momentum thickness are determined by the momentum- and energy-integral equations. The accuracy of the method is examined by comparing the results with exact solutions. Quartic velocity profile gives good results for decelerating main flows, while the Hartree velocity profile proves to be satisfactory for accelerating main flows.