The birthday spacing test is an extension of the iterated spacing test described by Marsaglia in 'A current view of random number generators, Keynote Address, Statistics and Computer Science: XVI Symposium on the Interface, Atlanta, Proceedings, Elseiver'. If m birthdays are randomly chosen from a year of n days, then sorted, the number of duplicated values with parameter l = m3 /(4n). Extensive simulation with a variety of RNG's provides values of m and n for which the limiting Poisson distribution seems satisfactory. Among these is m = 1024 birthdays for a year of length n = 224 with l = 16, the version used in diehard, and more stringent versions, n = 232, 231, 230, 224, 222, 215; m = 4096, 4096, 4096, 1024, 512, 128.