A complete statistical description of the properties of a cellular microstructure generated by a three-dimensional Poisson-Voronoi tesselation has been obtained by a rigorous computer simulation involving several hundred thousand cells. A two-parameter gamma distribution is found to be a good fit to the cell's face, volume, and surface area distributions. For a sample size of several thousand cells or less, a lognormal distribution can also be used to approximate these distributions. The individual face, area, and edge length distributions are also obtained.