The 1938 U.S. National Championships (now known as the US Open) was a tennis tournament that took place on the outdoor grass courts at the West Side Tennis Club, Forest Hills in New York City, United States. The tournament was scheduled to be held from Thursday September 8 until Saturday September 17 but was prolonged until Saturday September 24 due to poor weather caused by the 1938 New England hurricane. It was the 58th staging of the U.S. National Championships and the fourth Grand Slam tennis event of the year. American Don Budge won the men's singles title and became the first tennis player to win the Grand Slam i.e. winning all four Major tennis tournaments (Australian Championships, French Championships, Wimbledon Championships, and U.S. National Championships) in a single calendar year. Budge also won the doubles and mixed doubles title.

Finals

Men's singles

🇺🇸 Don Budge defeated 🇺🇸 Gene Mako 6–3, 6–8, 6–2, 6–1

Women's singles

🇺🇸 Alice Marble defeated 🇦🇺 Nancye Wynne Bolton 6–0, 6–3

Men's doubles

🇺🇸 Don Budge / 🇺🇸 Gene Mako defeated 🇦🇺 Adrian Quist / 🇦🇺 John Bromwich 6–3, 6–2, 6–1

Women's doubles

🇺🇸 Sarah Palfrey Cooke / 🇺🇸 Alice Marble defeated 🇫🇷 Simonne Mathieu / 🇵🇱 Jadwiga Jędrzejowska 6–8, 6–4, 6–3

Mixed doubles

🇺🇸 Alice Marble / 🇺🇸 Don Budge defeated 🇦🇺 Thelma Coyne Long / 🇦🇺 John Bromwich 6–1, 6–2