High-resolution numerical experiments using a three-dimensional non-hydrostatic model with horizontal grid size of 5 or 2 km are performed to clarify what determines the structure and cloud pattern of polar lows. An axisymmetric initial vortex is imposed in a baroclinic basic state for which thermal wind balance holds. It is found that when the baroclinicity is absent, a hurricane-like vortex with spiral cloud bands, a cloud-free eye, and a warm core develops. When the baroclinicity is strong, on the other hand, a vortex with a comma-shaped cloud and slightly larger horizontal scale develops. The former appears to develop due to CISK/WISHE mechanism, while the latter due to baroclinic instability modified by latent heating.