The sural nerve is formed by the union of the medial sural cutaneous nerve, which is a branch of the main trunk (the tibial nerve), and the common fibular communicating branch of the lateral sural cutaneous nerve, which is a branch of the common fibular nerve. Anatomical variations in the formation of the sural nerve are common, although the topographical localization of this nerve is constant. In this report, we describe three cases of an anomalous course of the medial sural cutaneous nerve which descended through the gastrocnemius via a tunnel formed within the muscle. Such anatomical variations of the sural nerve are clinically important when evaluating sensory axonal loss in distal axonal neuropathies since sural nerve mononeuropathy is less likely to occur.