BANGKOK , Thailand ( CNN ) -- Thailand 's King Bhumibol Adulyadej , the world 's longest-reigning monarch , has been hospitalized with fever and fatigue , the royal palace said Sunday . King Bhumibol Adulyadej attends a celebration of his 81st birthday in Bangkok on December 2 , 2008 . King Bhumibol Adulyadej , 81 , was admitted to a Bangkok hospital on Saturday night . Doctors are monitoring his condition while administering antibiotics and intravenous fluid , the statement from the Royal Household Bureau said . The statement was carried by Thai News Agency and other local media . The king was formally crowned on May 5 , 1950 . Watch why king 's health is big issue » . Thailand abolished absolute monarchy in the 1930s , so the king wields little power although he last month appealed for unity amid Thailand 's four-year-long political crisis . He remains a deeply revered figure and enjoys immense popularity . Prime Minister Abhisit Vejjajiva told reporters on Sunday that the king visited hospital on doctors ' advice . `` There is no problem with His Majesty 's conditions . From my chats with doctors , there is nothing to be concerned about , '' Abhisit said after signing a visitors ' log book at the hospital , according to Reuters.com .
Thailand 's King Bhumibol Adulyadej is diagnosed with cancer and pneumonia . King Sri Adulyadej is world 's longest - reigning monarch . King wields little power but is deeply religious and enjoys immense popularity .