Andersson began racing in the motocross world championships for the Husqvarna factory, finishing second behind Suzuki'sJoël Robert in the 1971 250cc motocross world championship. For the 1972 season, Andersson was hired by the Yamaha to help develop their new motorcycle with its innovative rear suspension using a single shock absorber called a monoshock. He again came in second place to Robert. By the 1973 season, Yamaha's monoshock suspension outclassed the competition, taking Andersson to his first world championship ahead of Adolf Weil and Heikki Mikkola Andersson was a member of the victorious Swedish 1974 Motocross des Nations team that included Bengt Aberg, Ake Jonsson and Arne Kring. In 1975, Andersson placed second once more behind Puch'sHarry Everts. For the 1976 season, he signed to ride for the Montesa factory in the 250 class, and in 1977, he rode a Montesa in the 500cc class. He returned to Husqvarna in the 1978 and 1979 seasons in the 500cc class.