The iliotibial band is a fibrous structure that runs longitudinally down the lateral thigh from the iliac crest to the anterolateral tibia just below the knee (Gerdy's tubercle). Iliotibial band syndrome, also called iliotibial band friction syndrome, is characterized by pain in the distal iliotibial band region. Any repetitive flexion / extension at the knee (eg, from running, cycling) can cause irritation at the distal iliotibial band.

The condition may be caused by friction between the iliotibial band and the lateral femoral condyle. Some have suggested there can be other causes for the pain, such as an inflamed bursa.