The crystal structure of a new monoclinic metastable phase of anthracene formed during vapor growth has been determined from single crystal X-ray data (DARCH-1 automatic diffractometer, Mo K-alpha radiation). This metastable anthracene phase crystallizes in the monoclinic space group P2(1)/n with a = 8.553(2), b = 6.021(1), c = 22.334(4), Angstrom and beta = 124.54(3)degrees, and four molecules per unit cell. All carbon and hydrogen atom positions have been determined and refined to R = 0.044 for 330 unique reflections.