Van Dyken is an asthmatic who suffered from severe asthma throughout her childhood and into adulthood. She began swimming on the advice of a doctor as a way to strengthen her lungs to cope with her condition and prevent future asthma attacks.

Van Dyken began her competitive swimming career at Cherry Creek High School in Greenwood Village, Colorado, where she was state champion and state record holder in the 50 yard freestyle and 100 yard butterfly in her Junior and Senior years, and where in 1991 she captained her team to a state title. At the 1992 US Olympic Trials, she placed 4th in the 50 meter freestlye, just missing the Olympic team. After high school, Van Dyken attended the University of Arizona for two years before transferring to Colorado State University, where she broke her first (of many more to come) United States record with a time of 21.77 seconds in the 50 yard freestyle at the NCAA championships in 1994. She also placed second in the 100 yard butterfly and the 100 yard freestyle to Olympian Jenny Thompson. In 1994 she was named the NCAA Female Swimmer of the Year. After college, she moved to the United States Olympic Training Center in Colorado Springs, CO, to train full-time for the 1996 Olympics.

At the 1996 Summer Olympics in Atlanta, GA, Van Dyken became the first female athlete in history to win 4 gold medals in a single Olympic games. Her success in swimming won her a wide variety of awards and accolades, including: the ESPN Awards (ESPY) Female Athlete of the Year award; Swimming World Magazine's female Swimmer of the Year award; induction into the Colorado Sports Hall of Fame; induction into the US Olympic Hall of Fame; named Associated Press Female Athlete of the Year, USOC Sports Woman of the Year, the Women’s Sports Foundation Sports Woman of the Year and USA Swimming Swimmer of the Year. She was also featured as one of Glamour magazine’s Top 10 Women of the Year, named one of 25 most influential females in sport by Women’s Sports and Fitness magazine and received the ARETE Courage in Sports award. She has graced the cover of several newspapers and magazines, including USA Today, Newsweek, Time, Swimming World Magazine, and Sports Illustrated. Van Dyken was a guest on Late Night with David Letterman, the Rosie O'Donnell Show, and the Today Show. She was featured in a Milk add with a photograph taken by world-renowned photographer Annie Leibovitz, and she was honored with her own Wheaties box.

She continued to compete after the 1996 Olympics, but was plagued by injury, including a shoulder injury which required several operations and which left her unable to train for over a year. She staged a comeback, however, and made the 2000 US Olympic Team in the 50 meter freestyle, the 4X100 Medley Relay and the 4X100 Freestyle Relay. At the Olympic Games in Sydney, Australia, Van Dyken won two gold medals in these latter two events, and placed 4th in the 50 meter freestyle. This brought here total career Olympic medal count to 6 gold medals. In addition to her Olympic accomplishments, Van Dyken won several World titles, American records, and world records.

Van Dyken is retired from swimming and lives with her husband, NFL punter Tom Rouen, in Colorado and Arizona. Since her retirement, Van Dyken has toured on a number of speaking engagements to groups as varied as schools and multi-national coorporations, she has been a DJ on a sports radio show in Arizona, served as the side-line reporter for the Seattle Seahawks football team, and even played in the award-winning stage-play the Vagina Monologues. She is actively involved in a number of charities, including the Make-A-Wish Foundation , and along with husband Rouen runs an annual celebrity fundraiser in Evergreen, Colorado to raise money for disadvantaged youth.