The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones,[1] or as a pair the sitting bones,[2] is a large posterior bony protuberance on the superior ramus of the ischium.

When sitting, the weight is frequently placed upon the ischial tuberosity.

[3] The gluteus maximus provides cover in the upright posture, but leaves it free in the seated position.

[4] The distance between a cyclist's ischial tuberosities is one of the factors in the choice of a bicycle saddle.

This article incorporates text in the public domain from page 235 of the 20th edition of Gray's Anatomy (1918)