Thomas Stephen Cullen (November 20, 1868 – March 4, 1953) was a Canadian gynecologist associated with Johns Hopkins Hospital. Born in , Ontario, Cullen was educated at the and the University of Toronto, graduating from the latter school with a Bachelor of Medicine degree in 1890. He began studying at Johns Hopkins University the next year, before traveling to Germany and studying at Johannes Orth's laboratory at the University of Göttingen in 1893. From 1893 to 1896, Cullen was in charge of gynecological pathology at Johns Hopkins, and in 1919 he was named a professor of clinical gynecology.