Steven Mark Asmussen (born November 18, 1965 in Gettysburg, South Dakota) is an American Thoroughbred racehorse trainer. Born into a horse racing family, his parents, Keith and Marilyn "Sis" Asmussen, are both trainers who operate El Primero Training Center off the Mines Road in Laredo, the seat of Webb County in south Texas. His older brother, Cash Asmussen, currently a trainer himself, is a retired Eclipse Award-winning jockey and a champion in Europe.
Asmussen began racing at age sixteen as a jockey, competing at racetracks in New Mexico, California, and New York for three years until his height and weight ended his riding career. In 1986 he began training Thoroughbreds and American Quarter Horses in New Mexico. In 2002, he led all trainers in Thoroughbred flat racing with 407 wins then in 2004 set a new record for wins by a trainer with 555, surpassing the previous standard of 496 held since 1976 by Jack Van Berg.
Steve Asmussen's colt, Curlin, finished third in the 2007 Kentucky Derby and beat out Derby-winner Street Sense to win the 2007 Preakness Stakes. Curlin finished second in the 2007 Belmont Stakes to filly Rags to Riches, and went on to take the Breeders' Cup Classic on October 27, 2007, at Monmouth Park in Oceanport, New Jersey. The Breeder's Cup is considered the "Super Bowl" of thoroughbred horseracing. Curlin's regular jockey is Robby Albarado.
Asmussen graduated from United High School in Laredo in 1985. He and his wife, Julie Marie Asmussen, have three sons. Asmussen's grandmother, Helen M. Asmussen, died at the age of eighty-three, on Mother's Day, 2007, and was buried on Thursday, May 17, two days before the Preakness victory. She followed every race that her grandsons entered.
Keith Asmussen told Tricia Cortez, formerly of the Laredo Morning Times that his fellow Laredoans do not "have a clue how big Laredo is and has been in the horse industry, and after today, it will be even quadrupled. Some of the best horses have been trained and conditioned in Laredo."
Asmussen is the first Laredoan to have a horse win any of the three legs of the Triple Crown.
In 2008, Asmussen won a single-season record of 622 races. On December 6, 2009, he surpassed his 2008 record with his 623rd race at Woodbine Racetrack near Toronto, Canada. Similarly, in 2004 he collected 555 victories to break his 2003 record. As 2009 neared its end, Asmussen had won more than $21 million in career purse earnings.
Horses Trained by Steve Asmussen 
- "Breaking his own record: Trainer Steve Asmussen sets a mark with 623rd victory of 2009", Laredo Morning Times, December 10, 2009, p. B1
- Trainer for Doctor Decherd, Private Vow and Storm Treasure
- Trained Gaff
- Steve Asmussen at the NTRA
- Tricia Cortez, "Winner by a nose: Trainer Steve Asmussen's Curlin takes Preakness", Laredo Morning Times, May 20, 2007
- Joe Drape, New York Times News Service, "Asmussen's horse powers way to Horse of the Year title", Laredo Morning Times, October 30, 2007
- Asmussen Has Drug Positive