Ernest Steven Monteiro CBE FRS BBM PJG FRFPS (21 December 1904 – 2 March 1989) was a Singaporean physician, specialised in preventive medicine.^[1] He also served as the Singapore Ambassador to Brazil, Cambodia and the United States.^[2]

Monteiro was educated in St Anthony's School, Raffles Institution and King Edward VII College of Medicine.^[1][3][4]

Monteiro started his medical career in Tan Tock Seng Hospital (TTSH) in 1929.^[3][4]

During the Japanese Occupation, Monteiro was Director of Middleton Hospital for Infectious Diseases, which was TTSH's infectious diseases wing and a predecessor of National Centre for Infectious Diseases in Singapore.^[5] He discovered that the available quantity of diphtheria antitoxin was depleting. He exposed live goats to diphtheria to create more antitoxin.^[5]

After completing his post-graduate studies on a Queen's Scholarship in 1949, he was elected head of Faculty of Medicine of the then University of Malaya, Singapore in 1956–1960.^[1][3][4][6]

In 1958, he started to use Sabin vaccine on a mass scale to protect young children and adults from polio to wipe-out beri-beri with Vitamin B-1 and eliminated diphtheria in children.^[1] By 1977, diphtheria and polio had become things of the past for Singaporeans.^[5]

Upon his retirement in 1965, he was appointed the Emeritus Professor and Pro-Chancellor of National University of Singapore.^[1] Monteiro taught many medical students from Singapore and Malaysia. Among his students were Tun Dr Mahathir Mohamed (former Prime Minister of Malaysia) and Tun Dr Siti Hasmah Mohamad Ali.^[1] He played a major role in establishing high standard of medical practice in Singapore.^[1]

Monteiro was appointed the first Ambassador of Singapore to Cambodia in 1966-1968 and to United States and Brazil in 1969–1976.^{[1][2][3][4][6]}

Monteiro came back home in 1977 and continued his private practice as a physician.^[1]

Monteiro died of liver failure on 2 March 1989.^[3][4] He divorced Una Marie Lewis, his first wife, in April 1971,^[7] and secretly married Ling Mie Hean in August 1971 in Washington.^[8] He has two sons (Dr Edmund Hugh Monteiro and Dr Gerald Monteiro) and 2 daughters (Jean and Irene) from the first marriage and a son, John Monteiro, from the second marriage.^[1]

Monteiro was appointed Commander of the Order of the British Empire (CBE) in 1957 Birthday Honours.^[9] The Republic of Singapore awarded him Bintang Bakti Masyarakat (BBM) in 1963 and the Pingat Jasa Gemilang PJG in 1968.^[1] He was also named a Fellow of the Royal Society in 1972 for the Promotion of Health for his achievements in preventive medicine.^[1] In 1973, he was awarded an International Award for Distinguished Service of the US National Kidney Foundation.^[1]