Summary: Ellipsometric measurements in the spectral range 250–850 nm have been made on polished single crystals of natural cuprite from Namibia and of artificial cuprite grown by a total-oxidation method from pure copper. Derived values of the refractive indices, absorption coefficients, normal reflectances, and the complex dielectric constants for the two materials are all closely similar, suggesting that the stoichiometry and purity are essentially the same. Values of the absorption coefficient at the red end of the spectrum are inconsistent with the observed transparency of the crystals, and are compatible with a 10 nm surface oxidation film of cupric oxide. This study is part of a wider survey of the effects of doping and stoichiometry on the optical parameters of cuprite.