A Russian tourist was found dead in his room in Pattaya, Chon Buri province on Sunday near midnight.
Police said Vladimir Shahmatov, 29, had been dead for about 10 hours. There were no signs of violence.
His friend told police that Shahmatov had been in Pattaya for about 20 days. They went out together on Sunday and Shahmatov later returned to his room.
There was no reply when his friend knocked at his door later in the day. He looked through the window and saw his friend on the floor. He then called a security guard, who opened the door but Shahmatov was already dead.