2009-10: Erik Karlsson skated for Frolunda's U18 and U16 teams in Sweden and competed for Goteborg 1 in the TV-Pucken tournament for high school age players. He scored 1 goal with 3 assists for Frolunda U18 in four games in Elit play and in nine games in Allsvenskan U18 play he had 1 goal and 2 penalty minutes. Karlsson appeared in one playoff game for Frolunda U18, which won a bronze medal. In eight U16 games he scored 3 goals with 3 assists and had 8 penalty minutes. In 8 games in the TV-Pucken tournament he had 3 goals and 3 assists. Gotborg 1 finished third in the tournament.
2010-11: Karlson split the season between Frolunda's U20 and U18 team and skated for Sweden's U17 team in five international contests. In 29 games in the SuperElit U20 league he had 4 goals with 9 assists and had 41 penalty minutes. He skated in seven playoff games for Frolunda, which won the U20 championship, and had 1 goal with 1 assist and 4 penalty minutes. In 26 games for the Frolunda U18 squad he scored 20 goals with 22 assists and had 12 penalty minutes. He played four U18 playoff games and scored 1 goal with 1 assist.
2011-12: Karlson appeared in 47 games with Frolunda's U20 team and represented Sweden in three tournaments - the 2011 U19 World Junior A Challenge, the 2011 U18 Ivan Hlinka Memorial Tournament and 2012 U18 World Junior Championship. Karlson scored 14 goals with 19 assists, was minus-four and was second on the team with 70 penalty minutes. In the two playoff games versus Linkopings he was scoreless and minus-one. Karlsson had 1 goal and 6 penalty minutes in four games at the World Jr A Challenge. Playing for Sweden's U18 team he had 1 assist in two games at the Ivan Hlinka event and scored 1 goal with 2 assists and was plus-two as Sweden reached the silver medal game of the U18 WJC. Karlsson was ranked 14th amongst European skaters in Central Scouting's final rankings prior to the NHL Draft and was selected by Carolina in the fourth round (99th overall).
Karlsson will likely stay in Sweden for a couple more season before making his way to North America.