2006-07: Dennis Rasmussen skated for the Vasteras U18 team in central Sweden and played for Vastmanland in the TV-Pucken tournament for high school age players. He scored 6 goals with 10 assists and 14 penalty minutes in 14 regular season games and scored 2 goal with 1 assist and 2 penalty minutes in five playoff games with Vasteras. In eight TV-Pucken games he scored 1 goal with 5 assists and 16 penalty minutes.
2007-08: Rasmussen skated for the Vasteras U20 team as a 17-year-old. He scored 8 goals with 11 assists and 38 penalty minutes in 39 regular season games and scored 1 goal with 2 assists and 8 penalty minutes in three playoff games.
2008-09: Rasmussen made his pro hockey debut — playing 15 regular season Allsvenskan games and five games in the Kvalserien for the Vasteras men’s team — and tied Eddie Davidsson with 44 points in the regular season to finish second on the Vasteras U20 team in scoring. He scored 2 goals with 1 assist and was +2 with 4 penalty minutes as Vasteras finished third in Allsvenskan. Rasmussen scored 3 goals with 1 assist during the Kvalserien. Vasteras failed to earn elevation to Elitserien; finishing last in the six team tournament. Rasmussen scored 19 goals with 25 assists — three points behind Jonas Puntusson for the team lead — and had 18 penalty minutes in 40 regular season games for the Vasteras U20 team. He scored 1 goal with 3 assists in four playoff games. He played eight games for the Sweden U19 team and scored 3 goals with 2 assists and 10 penalty minutes. Rasmussen was ranked 188th amongst international skaters in the CSS final rankings but was not selected in the 2010 NHL Draft.
2009-10: Rasmussen played in 44 of 52 regular season games for Vasteras in his first full season in Allsvenskan and was part of the Sweden U20 team that won a bronze medal at the 2010 World Junior Championship. He scored 4 goals with 13 assists and was -10 with 20 penalty minutes for Vasteras. The club finished tied for eighth with Boras HC and missed the playoffs. Rasmussen played eight games for the Vasteras U20 team, including five playoff games, and scored 2 goals with 7 assists and 31 penalty minutes. In six games at the WJC he scored 2 goals with 1 assist and was +3 with 2 penalty minutes. Rasmussen was ranked 109th amongst international skaters in the CSS final rankings but was not selected in the 2010 NHL Draft.
2010-11: Rasmussen was an assistant captain for Vasteras as a 20-year-old and was third on the team in total points. He scored 10 goals with 23 assists and was +10 with 16 penalty minutes in 48 regular season games. Vasteras finished fifth in Allsvenskan and was second in the four-team preliminary playoffs — missing out on an opportunity to play in the Kvalserien. Rasmussen scored 3 goals with 2 assists and was +2 in six preliminary series games.
2011-12: Rasmussen played for Vaxjo Lakers in his first season in the Sweden Elitserien and skated in four international games for the Sweden men’s team. He skated in all 55 games for the Vaxjo, averaging 16:38 minutes of ice time, and scored 8 goals with 9 assists; finishing minus-7 with 10 penalty minutes. The Lakers finished ninth — two points behind MODO for the final playoff spot. Rasmussen scored 1 goal with 2 assists and was +1 in four games with Team Sweden.
2012-13: Rasmussen was the second-leading scorer for Vaxjo behind one-time Atlanta Thrashers right wing Tomi Kallio and played for Sweden in six games during the Euro Hockey Trophy tournament. He led the Lakers with 16 goals and was minus-1 with 12 assists and 28 penalty minutes in 42 regular season games. Vaxjo finished 10th; missing the playoffs. Rasmussen had no points nor penalties and was minus-3 in six games for Sweden in tournament play.
2013-14: Rasmussen was an assistant captain for Vaxjo in his third season and finished tied for tenth in scoring in the re-christened SHL. In 52 games he scored 16 goals with 24 assists — tying Viktor Arvidsson of Skelleftea with 40 points — and was +6 with 20 points. The Lakers finished third in the regular season and defeated Lulea in the quarterfinals before falling to Farjestads in the semifinals. Rasmussen averaged 18 minutes of ice time per game in the playoffs, scoring 2 goals with 4 assists in 12 games, and was an even plus/minus with 6 penalty minutes. He played for the bronze medal-winning Sweden men’s team at the 2014 IIHF World Championship and had 1 assist in nine games. Chicago signed Rasmussen to an one-year entry-level contract on June 10th, 2014.
Chicago signed Rasmussen to an one-year entry-level contract on June 10th, 2014.