Tyler Hamilton career timeline

A timeline of events involving Tyler Hamilton, who is announcing his retirement from professional cycling after testing positive for the steroid DHEA:

• Member of NCAA cycling championship team at University of Colorado.

• Turns professional and signs with Montgomery-Bell cycling team, whose title sponsorship shifts to U.S. Postal Service the following year. Hamilton will ride for Postal through the 2001 season.

• Finishes 69th overall in his first Tour de France.

• Marries Haven Parchinski. Wins first international stage race at Tour of Denmark.

• Wins the Dauphine Libere, a key tuneup race for the Tour de France. Finishes 25th in the Tour, the next-highest U.S. rider after winner Lance Armstrong.

• Jumps to Denmark-based CSC team as leader. Finishes second in Giro d'Italia (Tour of Italy) despite hairline fracture of left humerus and torn tendon in shoulder suffered in crash. Grinds teeth because of pain and has to have 11 of them capped.

• Wins Tour of Romandie and Liege-Bastogne-Liege classics. Signs on as featured protagonist in IMAX movie "Brain Power." Fractures collarbone in mass pileup at finish of Stage 1 of the Tour de France. Continues to race, wins Stage 16 in a solo breakaway and finishes fourth overall in what turns out to be his best Tour performance.

• Jumps to Switzerland-based Phonak team. Wins Tour de Romandie. During a star-crossed Tour de France, his dog has to be euthanized, and back injuries sustained in a Stage 6 crash force Hamilton to pull out of the race several days later. Recovers in time to compete in Athens Olympics and wins a gold medal in the time trial.

In September, he wins time trial stage in Vuelta d'Espana (Tour of Spain), then withdraws from the race, citing a stomach ailment. International authorities announce his blood sample has tested positive for homologous transfusion, meaning another person's blood type was present in his system. Teammate Santiago Perez tests positive for the same offense at the same race. Authorities also reveal Hamilton's A sample at the Olympic Games showed similar evidence, but improper storage of the B sample precluded the result from being confirmed; they further contend Hamilton was warned his blood markers had been suspicious since earlier that season. Hamilton is allowed to keep his gold medal. He denies any wrongdoing and decides to fight the Vuelta test result.

• Hamilton's defense team argues the test for transfusions is not reliable, and offers several alternative explanations for the presence of foreign blood cells in his body, including the so-called "vanishing twin" theory. However, his positive test is upheld 2-1 by an arbitration panel. He receives a mandatory two-year suspension backdated to September 2004.

• The Court of Arbitration for Sport unanimously rejects Hamilton's appeal. In June, documents surface in the Operacion Puerto doping probe in Spain that link Hamilton to a Madrid blood doping operation run by Dr. Eufemiano Fuentes and indicating a financial arrangement between the two from 2002-04. The Spanish newspaper El Pais publishes documents including a doping "calendar" that corresponds with Hamilton's race schedule, and a faxed invoice that bears his wife's maiden name and their home phone number in Girona, Spain. Hamilton is said to have used transfusions, human growth hormone, testosterone, EPO and insulin in an effort to aid performance. Hamilton denies working with Fuentes and is never charged in connection with the case.

• Hamilton signs with Russian-sponsored Tinkoff, struggles early in the season and makes his U.S. return at the Tour of Georgia in April. Shortly afterwards, Tinkoff suspends him because of his links to the Puerto case, triggering a court battle that is still pending. Hamilton considers retiring, but is approached late in the year by U.S.-based Rock Racing team owner Michael Ball and signs with the maverick squad.

• Hamilton and two Rock Racing teammates are barred from starting the Tour of California by race organizers, who cite the fact there are open investigations against them. The riders accompany the team along the route, training and signing autographs. In July, Hamilton wins the Tour of Qinghai in China, and follows that up in late August by sprinting around Garmin-Chipotle rider Blake Caldwell to win the U.S. national road championships in a photo finish. He and wife Haven divorce. His mother Lorna is diagnosed with breast cancer.

• Hamilton finishes 83rd in the Tour of California, more than an hour off winner Levi Leipheimer's pace, and is awarded the "Most Courageous Rider" jersey: "courage, sacrifice, inspiration, determination and perseverance" for his efforts in a breakaway during Stage 4. Withdraws from two races on his schedule, citing bronchitis.

• During a teleconference on April 17, he will announce he is retiring immediately following a positive test for the steroid DHEA, which he said he knowingly ingested in an over-the-counter herbal antidepressant. Hamilton likely would face a suspension of eight years to life for his second offense.

Bonnie D. Ford covers tennis and Olympic sports for ESPN.com. She can be reached at bonniedford@aol.com.