The pudendal nerve is a considerably large branch of the sacral plexus. There are many articles in the literature concerning the pudendal nerve in adults, but as far as we know, there is none on the branching pattern and variations in pudendal nerve anatomy in fetus. This study investigates the pudendal nerve trunking with respect to the piriformis muscle in 25 formalin-fixed fetuses (50 sides of pelves, 15 females, 10 males), ranging from 20 to 37 weeks of gestation. We investigate pudendal nerve trunking in four types: Type I-a is defined as single-trunk with the inferior rectal nerve branching proximal to the dorsal nerve of penis/clitoris (38%), Type I-b is also single-trunk with the dorsal nerve of penis/clitoris branching proximal to the inferior rectal nerve (24%), Type II is double-trunk with medial trunk as an inferior rectal nerve (34%), and Type III is triple-trunk (4%). We measured the average diameter of the main trunk of pudendal nerve in Type I-a and I-b groups to be 0.98 +/- 0.33 mm. We also measured the average length of the pudendal nerve trunks before the dorsal nerve of penis/clitoris branch to be 7.35 +/- 3.50 mm. There was no significant statistical difference in the average length, diameter, number of trunks, and pudendal nerve variations between male and female and also right and left sides of the pelves. This first and detailed fetal study of pudendal nerve trunking with respect to the piriformis muscle would be useful for educational anatomy dissections and anatomical landmark definitions for relevant clinical procedures. Clin. Anat. 21:691-695, 2008. (C) 2008 Wiley-Liss, Inc.