Guldborgsund is a municipality (Danish, kommune) in Region Sjælland in Denmark, created on 1 January 2007 from six (6) former municipalities on the two islands Lolland in the west and Falster in the east bordering the Guldborgsund strait. It covers an area of 903.15 km² (2013) and has a total population of 61,007 (1 January 2014). Its neighboring municipalities are Lolland to the west and Vordingborg to the north. Its administrative seat is in the town of Nykøbing Falster.