We report measurements of Ξ - and Ξ + hyperon absolute yields as a function of rapidity in 158 GeV/c Pb+Pb collisions. At midrapidity, dN/dy=2.29+/-0.12 for Ξ - , and 0.52+/-0.05 for Ξ + , leading to the ratio of Ξ + /Ξ - =0.23+/-0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of T~300 MeV near mid-rapidity. The estimated total yield of Ξ - particles in Pb+Pb central interactions amounts to 7.4+/-1.0 per collision. Comparison to Ξ - production in properly scaled p+p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Ξ - production in Pb+Pb central collisions over elementary hadron interactions.