Cohen was appointed by President Ronald Reagan as Judge, United States Tax Court, on September 24, 1982, for a term ending September 23, 1997. She served as Chief Judge from June 1, 1996 to September 23, 1997, and was reappointed by President Bill Clinton on November 7, 1997, for a term ending November 6, 2012. She served again as Chief Judge from November 7, 1997 to May 31, 2000. She took senior status on October 1, 2012. President Barack Obama nominated Tamara W. Ashford of Virginia to the U.S. Senate for a fifteen-year term, to succeed her.