- Not to be confused with Frognal, an area of Hampstead, North West London, which also has a Frognal House
Frognal House was purchased by Thomas Townshend in 1752 and became the residence of his son, Thomas Townshend, 1st Viscount Sydney, after whom Sydney, Australia was named. In 1915 the Marsham-Townshend family sold the house and 1,740-acre (7.0 km2) estate to the government.
The house is also famous for being the original building of the Queen's Hospital (later Queen Mary's Hospital), Sidcup, developed as the First World War's major centre for facial and plastic surgery, largely through the efforts of Harold Gillies. Opened in 1917, the hospital and its associated convalescent hospitals provided over 1,000 beds, and between 1917 and 1921 admitted in excess of 5,000 servicemen.
In 1974, a new Queen Mary's Hospital was built to replace the original Great War hospital, and since November 1999 Frognal House has been a residential and nursing home run by Sunrise Senior Living, their first location in the United Kingdom.
The house gave its name to the nearby Frognal Corner, once a crossroads where the Sidcup Bypass crossed Perry Street and, since 1987, a grade-separated junction at the intersection of the A20 and the A222.