Diane Sawyer will become the second-ever female evening news anchor when she takes over "World News" in January for Charles Gibson, who announced his retirement today.

Gibson has been at ABC News for 35 years and says he plans to continue as an occasional contributor.

The two co-anchored "Good Morning America" from 1999-2006.

Gibson had been at the anchor desk since May of 2006, following the death of long-time host Peter Jennings, and the war-time injury to Bob Woodruff.

In an e-mail to ABC staff member Gibson said he had planned to retire at the end of 2007, but events including Jennings' death and Woodruff's injury compelled him to stay.

With Sawyer in her new role, two of the three leading anchors for the broadcast networks will be women. In 2006, Katie Couric became the first solo anchor of weekday evening news on a broadcast network.