No previous studies describe the anatomic relationship of the superior cluneal nerve to the posterior iliac crest and thoracolumbar fascia. In the current study, 15 cadavers were dissected to determine the relationship of the superior cluneal nerve to the posterior iliac crest and thoracolumbar fascia. The distances from the medial branch of the superior cluneal nerve to the posterior superior iliac crest and the midline were 64.7 +/- 5.3 mm and 81.0 +/- 9.2 mm, respectively. The distances between the level of the iliac crest and perforating points of the superior cluneal nerve on the thoracolumbar fascia were 5.8 +/- 1.8 mm inferiorly for the medial branch, 2.2 +/- 1.8 mm superiorly for the intermediate branch, and 12.0 +/- 4.4 mm superiorly for the lateral branch, respectively. The proximal dissection above the perforating point of the nerve showed that the medial branch of the superior cluneal nerve is confined within a tunnel consisting of the thoracolumbar fascia and the superior rim of the iliac crest as it passes over the iliac crest. The intermediate and lateral branches of the superior cluneal nerve either pierce the thoracolumbar fascia or pass through an orifice or fissure in the thoracolumbar fascia. In two specimens, the medial branches of the superior cluneal nerve were constricted within the osteofibrous tunnel. The nerve was entrapped between the rigid fibers of the thoracolumbar fascia and the iliac crest.