Patty and Cathy Lane were "identical cousins" on The Patty Duke Show. Both characters were played by Patty Duke.
The Patty Duke Show is an American sitcom which ran on ABC from September 18, 1963 until May 4, 1966, with reruns through August 31, 1966. The show was created as a vehicle for rising star Patty Duke, who had recently won an Academy Award for The Miracle Worker. A total of 104 episodes were produced, most written by Sidney Sheldon.