A patellar prosthesis has a hollow body portion providing a convex articulating surface on one side and a mounting chamber on its opposite side which provides a peripheral seating rim. An anchoring stem is attached to the body portion within the mounting recess and extends in a direction outwardly thereof and terminates in a flat base plate. The stem is formed of a pair of webs intersecting at a right angle to each other. The hollow body and cruciate cross section stem construction provides a light weight prosthesis which can be securely implanted on a patella which has been resected to provide a raised land portion having a central recess by fitting the seating rim on the raised land. A surgical cement is employed to help secure the prosthesis in place.