Regular perturbation solutions are obtained for the Stokes flow field, the first order effects of inertia on the flow field, and the primary and secondary pressure fields in the circular lid driven cavity. The physical mechanism that causes vortex breakdown exists at small Reynolds number; it is a stagnation of the secondary flow by an adverse pressure gradient. The discontinuity between the rotating lid and the stationary sidewall has negligible influence on the flow field provided that the inertial forcing of the secondary flow is not localized near the boundary discontinuity, and the Reynolds number is small.