This chapter provides a list of eponymous terms and rare diseases. These include acanthosis nigricans, which is pigmentation of the axillary skin associated with breast or gastric cancer; Baker’s cyst, which is almost always associated with knee joint pathology such as arthritis or torn meniscus; and Cloquet’s (Callisen’s) hernia, which is a deep femoral hernia that cannot protrude from the saphenous opening as it lies deep to the femoral vessels. The chapter then deals with DeQuervain’s disease, encephalocele, and familial adenomatous polyposis (FAP). It also describes gamekeeper’s thumb, hereditary osteodystrophy, inspissated bile syndrome, Jansen’s disease, Kaposi’s sarcoma, and livedo reticularis. Finally, the chapter defines McMurray’s test, which is used to identify medial meniscal tears; nutcracker oesophagus, which is an alternative name for diffuse oesophageal spasm; and osteogenesis imperfecta, which is an inherited collagen disorder, resulting in fragile bones that fracture easily, blue sclera, deafness, and soft teeth.