Abstract The isotropic to nematic transition in bowlic liquid cyrstals are theoretically examined with the help of the work by Krieger and James on a molecular crystal model. In addition to the conventional non-polar nematic phase, a polar nematic phase can also exist. The polar nematic–isotropic and the polar nematic–nonpolar nematic transitions can he either first or second order, and two tricritical points as well as one triple point exist (while the nonpolar nematic–isotropic transition is always first order).