Single crystals of pentaerythritol, a molecular crystal of the tetragonal system, were analysed by variable angle spectroscopic ellipsometry in the 1.5-5 eV spectral range. The dispersion of the ordinary refractive index n(o), i.e. for light propagating along the optic axis, and of the extraordinary one n(e) is modeled by the Cauchy formula and the spectra obtained over the complete range. (C) 2003 Elsevier B.V. All rights reserved.