Reto Grütter entered the sidecarcross world championship in 2003 as a nineteen-year-old in the French GP in Pernes Les Fontains, 27 April 2003, becoming the passenger for his countryman Ueli Müller.

Grütter won his first GP on 9 April 2007 in the season opener in Oldebroek, Netherlands.

In the 2008 season, Grütter continued to race with Willemsen[1] but an injury prevented him from taking part in the first race of the season and Willemsen replaced him with Bruno Kaelin for the first round.

[2] The team took out the 2008 world championship with a 97-point margin to second-placed Kristers Sergis.

He raced with Andy Bürgler in the 2009 Swiss championship, winning the national title comfortably.