Founded in 1903 by American Episcopal missionary Charles Brent, St. Luke's Hospital started as a nine-bed ward and dispensary named Mosher Hall. In 1907, it became the University Hospital. Over the next three decades, bed capacity at St. Luke's Hospital increased to 140 beds. During the Japanese Occupation, the hospital's name was changed to Nippon Byoin.
On February 1902, an 8-bed hospital called the Baguio Sanatorium - with a pioneering staff composed of American physicians, army nurses and hospital corpsmen headed by Dr. J. B. Thomas -- was established. It was set up as part Bureau of Civil Hospitals and Sanatorium of the Philippines primarily to serve the health needs of government officials, employees and American soldiers on vacation amidst pine trees in the cool climate of Baguio. A month later, the construction of a 15-bed capacity hospital consisting of six, three-room cottages was started.