An official statement from the Royal Household Bureau said an ailing King Bhumibol Adulyadej returned to Siriraj Hospital for a regular checkup. The statement did not say when or if he would return to the seaside city of Hua Hin.
Bhumibol, the world's longest-reigning monarch, has resided in Siriraj on and off for years. His last stay lasted seven months after having his gallbladder removed.
Thais hold great affection for Bhumibol, who was crowned on May 5, 1950, after coming to the throne in 1946 following the death of his elder brother.
Bhumibol has faded from public life over the past several years, though, and on his rare outings looks visibly frail and does not speak publicly.