Cuban epidemiologist who discovered that yellow fever is transmitted from infected to healthy humans by a mosquito. Although he published experimental evidence of this discovery in 1886, his ideas were ignored for 20 years.

A graduate of Jefferson Medical College, Philadelphia (1855), he returned to Cuba, where he practiced medicine in Matanzas and Havana. In 1879 Finlay was appointed by the Cuban government to work with the North American commission studying the causes of yellow fever, and two years later he was chosen to attend the fifth International Sanitary Conference in Washington, D.C., as the Cuban delegate. At the conference, Finlay urged the study of yellow fever vectors, and soon afterward he stated that the carrier was the mosquito Culex fasciatus, now known as Aedes aegypti.

In 1900 the U.S. Army Yellow Fever Board, which was headed by the physician Walter Reed (Reed, Walter), arrived in Cuba, and Finlay attempted to persuade Reed of his mosquito-vector theory. Although skeptical, Reed decided to investigate the idea, refining Finlay's experimental procedures in the process. Reed's proof that mosquitoes do indeed transmit yellow fever (1900) and William Gorgas' eradication of the disease in Cuba and Panama followed. Finlay was appointed chief sanitation officer of Cuba (1902–09), and after his death the Finlay Institute for Investigations in Tropical Medicine was created in his honour by the Cuban government.