The knee joint is a complex anatomical structure playing host to a wide variety of pathological processes. Knowledge of the anatomy of the synovial recesses and plicae relating to the knee is important, as the appearance of pathology in these unusual locations may, even for commonly encountered conditions, lead to diagnostic uncertainty. This review article discusses the magnetic resonance imaging (MRI) anatomy of the knee joint with an emphasis on the synovial recesses and plicae. The MRI appearance of a variety of synovial and osteochondral diseases that may involve these sites is illustrated.