243 or variant, may refer to:
- 243 Ida, a main-belt asteroid, the 243rd asteroid registered
- 243P/NEAT (Comet NEAT 243), a periodic comet, the 243rd periodical registered
- Lebo–Waverly USD 243, Kansas, USA; a unified school district, #243
- NA-243 (Karachi East-II), Pakistan; a national assembly constituency
- Collholme No. 243, Alberta, Canada; a municipal district
- No. 243 Squadron RAF (UK)
- 243rd Aviation Company, U.S. Army (USA)
- VMSB-243, Marine Scout Bombing Squadron (USA)
- 243rd Air Traffic Control Squadron USAF (USA)
- 243 Provost Company, Royal Military Police (UK)
- 243 (The Wessex) Field Hospital, Royal Army Medical Corps (UK)
- 243 Construction Squadron, Royal Engineers (UK)
- 243rd Guards Motor Rifle Regiment, Red Army; a Soviet Cold War unit
- 243rd Rifle Division, NKVD, Red Army; a Soviet unit in WWII
- 243rd Static Infantry Division (Wehrmacht), WWII Germany
- 243rd Coast Artillery (United States), Rhode Island National Guard interwar unit
- 243d Aero Squadron, U.S. Army Air Corps, an interwar unit
- 243rd Battalion, CEF, WWI Canadian Army unit
- 243rd Infantry Division (German Empire), WWI