U.S. senator Larry Craig (R- Idaho) announced his resignation Saturday, in the wake of a homosexual scandal in an airport men's room.
"I apologize for what I have caused," Craig said in a statement made in his home state.
U.S. media revealed Monday that Craig was arrested in June in a men's room at Minneapolis-St. Paul International Airport, and has pleaded guilty to misconduct.
He was fined more than 500 U.S. dollars and placed on unsupervised probation for a year.
According to a police report, a plainclothes police officer investigating complaints of sexual activity in the bathroom arrested the senator on June 11 after what the officer described as sexual advances made by Craig from an adjoining stall.
Although the senator denied that he is a gay, the Republican leadership denounced his behavior and asked him to step down.
Craig's resignation won't affect the makeup of the Senate since Idaho's governor is expected to name another Republican to replace him.
But the scandal adds to the difficulties that the Republican Party faces in trying win back control of the Senate in next year's elections.
Craig, 62, has represented Idaho for 25 years in the Senate and had planned for re-election.
He is the second Republican senator in recent weeks to find his personal behavior under scrutiny.
Senator David Vitter, (R-Louisiana), was implicated in a separate case when his phone number turned up in the records of an escort service that the authorities have described as a prostitution ring.