Development of the pelvic plexus is studied in 15 human embryos and 2 fetuses ranging in size from 4 to 132 mm. C.R. length. A tridimensional reconstruction of the entire pelvic block was made in two specimens (30 and 132 mm. C.R. length) 80 X. The first ganglionic elements appear in Carnegie's stage 16, but the real definition of what in the final anatomy of the plexus is described as the hypogastric ganglion (Lee-Frankenhäuser) is formed in stage 18. Complete development of the plexus occurs in stage 23. Other relevant facts are: the appearance in stage 18 of the pelvic splanchnic nerves, which are formed from S2, S3 and S4, the involvement of S1 and S5 were not observed in any case. In all specimens studied, a close proximity was seen between the pelvic plexus and genitourinary organs. Starting in stage 18, the terminal ureter consistently crosses the posterosuperior part of the pelvic plexus.