Viacom says Judy McGrath, the CEO and chairwoman of MTV Networks, is stepping down and a replacement has not yet been named.

Viacom Inc. said Thursday that with McGrath’s departure the executives in charge of MTV’s operating units, including the kids’ channel Nickelodeon, will report to Viacom CEO Philippe Dauman.

McGrath began her career with the company as a copywriter at MTV in 1981. She was named CEO and chairwoman of MTV Networks in July 2004.

The New York company did not give a reason for her departure.

MTV has enjoyed a resurgence recently thanks to hit shows such as “Jersey Shore” and “16 and Pregnant.”