Viljanmaa, who started for the Parkanon Urheilijat, ran for the first time in the Continental Cup in Ilomantsi in December 1994 and finished 40th over 5 km classic. She made her debut in the cross-country skiing world cup in March 1998 in Lahti , which she finished in 53rd place over 15 km freestyle. In February 2000 she got her first World Cup points in Falun with the 25th place in the 10 km freestyle. In the following year she won the Continental Cup for the first time in Mäntyharju over 5 km freestyle. In the 2001/02 season she came in the points eight times in the World Cup. Her best placement was 14th place in the Birkebeinerrennet . At the season highlight of the 2002 Winter Olympics in Salt Lake City , she achieved 37th place over 10 km classic and 24th place over 30 km classic. She finished the season in 40th place in the overall World Cup. At the beginning of the 2002/03 season she won her first and only World Cup victory in Kuusamo with the mixed relay. In the further course of the season she came six times in the top ten. She achieved her only podium finish in the World Cup singles in Oslo with second place over 30 km classic. At the Nordic World Ski Championships in 2003 in Val di Fiemme , she achieved 11th place over 10 km classic and seventh place in the 15 km mass start race. At the end of the season she finished 17th in the Sprint World Cup and 15th in the overall World Cup. These are her best overall results in the World Cup. Her best individual result in the World Cup in the 2003/04 season was 17th in the skiathlon in Kuusamo and in Ramsau am Dachstein . In 2003 and 2004 she won the 58 km classic Birkebeinerrennet. In the 2004/05 season she won the Scandinavian Cup in Veldre in the sprint and over 10 km classic and thus achieved fifth place in the overall standings. At the Nordic World Ski Championships in Oberstdorf in 2005 , she came 19th in the mass start race over 30 km classic. In March 2005 she was second in the Birkebeinerrennet. In her last active season 2005/06 she came in nine appearances in the Scandinavian Cup, eight times in the top ten. She achieved second place in Vuokatti over 10 km and, at the end of the season, second place in the overall standings. In addition, she was fifth in the König-Ludwig-Lauf and second in the Birkebeinerrennet in the season , taking sixth place in the overall ranking of the Marathon Cup . She completed her 66th and last individual World Cup race in March 2006 in Mora , which she finished in 17th place in the 45 km mass start race.