You Won’t Believe Why Last Names End in “Son” or “Sen”

9 June 2015
by Ancestry® Team

What does a name ending in -son or -sen tell us about our ancestors and where they came from in Scandinavia?

First, we know that this sort of last name is a patronymic, a surname formed by adding -son to someone’s father’s name, and it means “son of.” Trace such a name back far enough, and you’ll find that someone named John Carlson, for instance, was John, son of Carl. This type of name was also sometimes created with the addition of the suffix -dottir, meaning daughter; someone named Kari Olafsdottir would have been Kari, the daughter of Olaf.

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When laws eventually required families in the various Scandinavian countries to decide on a heritable surname — one that would pass down intact instead of changing every generation — many families adopted a current name as their hereditary family surname. This is known as a “frozen patronymic.”

You cannot determine where your ancestors come from merely by how their last name is spelled, but there are some common patterns that might give you hints as you research your family tree on Ancestry.


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Old-style patronymics were outlawed in Denmark in the 1820s, meaning that if you are researching Danish ancestors before then, keep in mind that the surname likely changed with every generation. Even though heritable surnames were mandated in the 1820s, it was still more than 50 years before the change was consistent; most Danes did not actually adopt fixed surnames until the mid- to late-1800s. Many Danish people who have the same patronymic surname, therefore, are not necessarily related.

Danish people generally use -sen (or just -s, as in Johns instead of Johnsen) for a son and -datter or -sdatter for a daughter. Southern Danes sometimes used -sen or -s for a daughter, as well.

Danish surnames ending in -sen are the most common type of Danish surname these days. In the U.S., descendants of Danish and Norwegian immigrants often have similar names that end in -sen, though some people in the U.S. have changed the spelling to -son.


Originally, the most common surnames in Norway were patronymic ones ending in -ssen or -sson or -sdatter or -sdotter (though the extra s is sometimes dropped). It was only in 1923 that, by law, each family was ordered to take a hereditary surname.

While most families adopted a patronymic name as their surname, some took the name of a farm where they lived or the name of another place name as their surname: Berg (mountain), Haugen (hill or mound), or Hagen (enclosed pasture), for example.

Keep in mind that it’s not uncommon for the first American generation of Norwegian immigrants to choose a different surname than the one their parents used. Their siblings might choose different names or spellings as well. Note, too, that the spelling in U.S. census records is often a phonetic approximation. Many earlier immigrants were illiterate, as Norway did not have public education until 1860, and there may not have been a standard spelling of a family’s surname.


Sweden passed the Names Adoption Act in 1901, requiring heritable surnames that are passed down to each generation. Before that, surnames were typically patronymic.

As of 1901, many people took a patronymic surname to pass down, and patronymics are still the most common Swedish names. Most often they end with -sson, but sometimes in the U.S., they are reduced to a single s (for example, what was Andersson became Anders in the U.S.). Some Swedish names use -dotter or -sdottir for a girl.

Some Swedish families, when they were required to adopt a surname, took names referring to places in nature, such as Lindberg (linden [lime] + berg [mountain]). Other Swedish surnames came from craftsmen taking names related to their trade or retired soldiers keeping names they were given in the military, such as Skold (shield) or Stolt (proud). Another source of Swedish names: up to about the 18th century, the clergy took Latinized names, which were based on their place of birth.

It’s important, too, to realize that as immigrants arrived in the United States, they may have translated or Anglicized their names to sound more English (i.e., Eastman instead of Ostman). Or the wife may have taken her husband’s name so it would not be misconstrued by their patronymic (and dissimilar) surnames that they were not married. Some families even adopted American surnames when they arrived in the U.S.

These are not hard-and-fast “rules,” and you cannot definitively place your Scandinavian family’s place of origin from a suffix on their last name. But you might be able to get some hints as to where they started out by starting a free 14-day trial with

— Leslie Lang