Andersen is a Danish-Norwegian patronymic surname meaning "son of Anders" (itself derived from the Greek name "Ανδρέας/Andreas", cf. English Andrew). It is the fifth most common surname in Denmark, shared by about 3.2% of the population.

From the same root - the given name Andreas - derives the surname Andreasen (cognate Andreassen) and Andresen .

The numbers of bearers of the surnames Andersen, Andreasen, Andreassen and Andresen in Denmark and Norway (2009):

Andersen Andreasen Andreassen Andresen source
Denmark 165,871 12,013 2,430 4,508 Statistics Denmark
Norway 38,433 103 12,376 6,581 Statistics Norway

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