The 20/20 co-anchor said in a statement obtained by PEOPLE that she checked into a treatment facility this weekend while on vacation.
"As so many other recovering alcoholics know, overcoming the disease can be a long and incredibly difficult process," Vargas said. "I feel I have let myself, my co-workers and most importantly my family down and for that I am ashamed and sorry."
Vargas, who's married to Marc Cohn and has two children with the singer-songwriter, said she was "committed to battling and addressing this debilitating disease" and expressed thanks for the support she has received.
The network said in a statement that it stands "squarely behind her" and was focused on Vargas's health.
"We look forward to having her back at ABC News when she feels ready to return," ABC News said.
Vargas, 51, spent several weeks in a treatment facility last fall. She acknowledged in an interview that aired in January on Good Morning America that she was an alcoholic and that it took years for her to admit it.
She said she had suffered panic attacks since she was a child.
"I dealt with that anxiety, and with the stress that the anxiety brought, by starting to drink," she said in the interview.
Vargas has worked in network news since 1993, first with NBC and then ABC, which she joined in 1996.
Additional reporting by PATRICK GOMEZ