The triangular fibrocartilage complex (TFCC) is a complex anatomic and biomechanical structure. Injury to the TFCC is a recognized cause of ulnar wrist pain. The TFCC may be injured in its horizontal portion, in its peripheral portions, or at its attachments. In the Palmer classification, TFCC lesions are categorized as traumatic or degenerative. Traumatic lesions are subclassified according to the location of the injury; degenerative lesions are subclassified according to the extent of degeneration. This classification is helpful in determining the mechanism of injury and directing clinical management. Magnetic resonance (MR) imaging may be more useful than arthrography in prospective evaluation of TFCC lesions. MR images accurately demonstrate the structural abnormalities that contribute to ulnocarpal instability and pain. The presence or absence of chondromalacia is a factor in the Palmer classification and is also considered in treatment planning. However, only advanced cases of chondromalacia are reliably detected with MR imaging.