Sterols extracted from Xanthoria parietina with organic solvents and released by saponification of the residual lichen tissue were analysed by GC-MS. The main components of the solvent-extractable sterols were two C28 trienes and those of the more tightly bound sterols were ergost-5-en-3β-ol and two C29 compounds. The structures of the C28 compounds were shown to be ergosta-5,7,22-trien-3β-ol, Ia (ergosterol) and the previously unreported ergosta-5,8,22-trien-3β-ol, IIa, for which the name lichesterol is proposed. The main C29 sterol was identified as (24R)-24-ethylcholesta-5,22-dien-3β-ol (poriferasterol).