Medical devices or components thereof, and particularly intracorporeal devices for therapeutic or diagnostic uses, which are formed at least in part of a polymeric material and a ferromagnetic or paramagnetic material, so that the medical device or component thereof is visible on magnetic resonance imaging (MRI) scans. In one embodiment, the medical device is a balloon catheter having an MRI visible balloon. In a presently preferred embodiment, there is an insufficient amount of the ferromagnetic or paramagnetic material within a wall of the balloon or coated onto a wall of the balloon to make the balloon radiopaque.