A nonlinear model has been developed to assess the time-dependent evolution of an axisymmetric liquid jet using a boundary element method. Vorticity trans- ported from the boundary layer in the oriflce passage to the free surface is modeled using a potential ring vortex placed at the oriflce exit plane. The vortex- strength is approximated using information from a Navier-Stokes solution (or equivalent) of the oriflce in- ternal flow. It is observed that the primary breakup can occur even without the presence of the gas phase. Using a secondary stability analysis after Ponstein's,23 the size of droplets is estimated based on the size of the ring-type structures shed from the periphery of the jet. Computed droplet sizes are in reasonable agree- ment with experimental data.