Disease involving the median nerve, from its origin at the BRACHIAL PLEXUS to its termination in the hand. Clinical features include weakness of wrist and finger flexion, forearm pronation, thenar abduction, and loss of sensation over the lateral palm, first three fingers, and radial half of the ring finger. Common sites of injury include the elbow, where the nerve passes through the two heads of the pronator teres muscle (pronator syndrome) and in the carpal tunnel (CARPAL TUNNEL SYNDROME).