A statement from the Prime Minister's Office says the 89-year-old Lee was admitted to Singapore General Hospital on Friday after experiencing a suspected transient ischaemic attack, which occurs when blood flow to the brain stops for a period of time. The condition is associated with irregular heartbeats.
The statement says Lee is recovering but will remain in the hospital for a few days.
Lee became prime minister in 1959 and saw the country through self-rule under the British, a two-year federation with Malaysia and independence in 1965. He remained in office until 1990, overseeing a period of rapid development that turned Singapore into a darling of foreign investors.
Lee's son Lee Hsien Loong is the current prime minister.