The objective of this pictorial essay is to illustrate the MR appearance of the common peroneal nerve and the appearance of masses that have been associated with peroneal nerve entrapment. Four human cadaveric knees underwent axial MRI utilizing a T1-weighted SE sequence. One knee was dissected by an orthopedic surgeon and three knees were transversely sectioned, and the gross morphology of the common peroneal nerve and the perineural structures was evaluated and correlated with the MR images.