Disclosed herein is a nickel-titanium alloy comprising nickel, titanium, and at least one rare earth element. The nickel-titanium alloy comprises from about 34 at. % to about 60 at. % nickel, from about 34 at. % to about 60 at. % titanium, and from about 0.1 at. % to about 15 at. % at least one rare earth element. The nickel-titanium alloy may further include one or more additional alloying elements. In addition to radiopacity, the nickel-titanium alloy preferably exhibits superelastic or shape memory behavior. Medical devices comprising the nickel-titanium alloy and a method of making them are also disclosed.