  We demonstrate that rotationally symmetric chiral metasurfaces can support
arbitrarily sharp resonances with the maximum optical chirality determined by
precise shaping of bound states in the continuum (BICs). Being uncoupled from
one circular polarisation of light and resonantly coupled to its counterpart, a
metasurface hosting the chiral BIC resonance exhibits a narrow peak in the
circular dichroism spectrum. We propose a realization of such chiral BIC
metasurfaces based on pairs of dielectric bars and validate the concept of
maximum chirality by numerical simulations
