"I value my relationship with the citizens of Oklahoma's First Congressional District, whom I am privileged and honored to have served for the past eight years. So, I wanted to be open and honest on this tough situation," the conservative Republican said in his statement.
He said he checked himself in to the treatment center Thursday night.
Sullivan said in the brief statement that he would take a temporary leave of absence from Congress.
John Tidwell, a spokesman for Sullivan, declined to elaborate on the congressman's statement.
Sullivan first was elected to Congress in 2002 in a special election to replace Steve Largent, who made an unsuccessful run for governor.
Sullivan has acknowledged being arrested when he was 20 for public intoxication.
An aide to Sullivan said in 2002 that the new congressman was arrested when he was 17 on a misdemeanor assault charge for fighting with another teenager and at 18 for trespassing and loitering.
Court records later showed the scuffle was with an off-duty Tulsa police officer.