Rebecca Lee Crumpler was the first African-American woman to receive an MD in the United States. She worked as a nurse for 8 years before being admitted to the New England Female Medical College in 1860, graduating four years later.
See http://www.pbs.org/wgbh/amex/partners/early/e_pioneers_crumpler.html
See http://www.pbs.org/wgbh/amex/partners/early/e_pioneers_crumpler.html