The iliac fossa is a large, smooth, concave surface on the internal surface of the ilium (part of the three fused bones making the hip bone).

The iliac fossa gives origin to the iliacus muscle.

[1] The obturator nerve passes around the iliac fossa.

Below it there is a smooth, rounded border, the arcuate line, which runs anterior, inferior, and medial.

When the "left" or "right" adjective is used (e.g. "right iliac fossa"), the iliac fossa usually means one of the inguinal regions of the nine regions of the abdomen.