In accordance with the invention, there are provided medical devices with incorporated shape memory systems that allow a polymeric medical device to be inserted in a first conformation or configuration and revert to a second conformation or configuration. The invention is useful in allowing the easy insertion or implantation of a device followed by expansion of the device in order to be retained without expulsion from a body cavity, for example. In another aspect of the invention there is provided a medical device, such as a ureteral stent, that includes comprising an elongated member having a proximal end portion and a distal end portion joined by a body portion. The elongated member has an initial outer diameter. A retention construction serves for retaining the member within a bodily cavity. The member is formulated of a physiologically acceptable polymer capable of hydrating and expanding from the initial member outer diameter to form a final member outer diameter. The device can assume differing shapes and can exhibit different degrees of softening at different places along its length and possess shape memory so that it can be inserted in a first conformation or configuration and revert to a second conformation or configuration upon the occurrence of a triggering event such as hydration.