D-Day (Korean: 디데이; RR: Di Dei) is a 2015 South Korean television series that aired on JTBC on Fridays and Saturdays at 20:40 (KST) for 20 episodes beginning September 18, 2015.

After disobeying his previous hospital director, Park Gun (Lee Geung-young), he then meets Jung Ddol-mi (Jung So-min), an orthopedic resident from Busan who came to Seoul to transfer a patient.

Ddol-mi tries to meet professor Han Woo-jin (Ha Seok-jin), a cold robotics surgeon who works in Hae-seong's old hospital who saved her life when she was younger before going back to Busan.

Meanwhile, a sinkhole appears in Seoul followed by a big earthquake that blocks all access to the city, causing phones, electricity, and water to not function.

Hae-seong teams up with Ddol-mi to treat people, but soon medicine starts to run out.