After the 1968 season, MLB expanded and an expansion draft was conducted in which the new teams could select certain players from the established teams. The White Sox left Wilhelm unprotected, possibly because they did not believe that teams would have interest in a much older pitcher. On October 15, 1968, Wilhelm was chosen in the expansion draft by the Kansas City Royals as the 49th pick. That offseason, he was traded by the Royals to the California Angels for Ed Kirkpatrick and Dennis Paepke.