Diederik got the equestrian sport at an early age. His father Alex van Silfhout is a known national and international dressage rider and has his own stable at Lunteren.

In 2003 reached Diederik for the first time the podium at the Netherlands Championship for juniors and became 3rd with Luxform’s Olympus. He became reserve for the junior team that went to the European Championship at Saumur. In 2004 he ended individual 4^th and won team silver with Luxform’s Popeye. In 2005 he won the 3rd place at the Netherlands Championship and after that team gold and individual a 5^th place with Luxform’s Olympus. Diederik made his Grand Prix debut with the stallion Dalwhinnie’s Forum, which was driven before by his father Alex. A year later Diederik showed his riding talents with the approved KWPN stallion Paddox and won bronze at the Netherlands Championship national. Diederik won in a fantastic way individual- and team-gold with Paddox at the European Championships for juniors.

Furthermore Diederik have a lot of fantastic international results with various horses. At the Netherlands Championships in 2007 he won the bronze medal with Ruby, while the Netherlands Team (where Diederik was a part of) won the gold medal again at the European Championship. At the Netherlands Championship in 2008 Diederik climbed on to a silver medal, again with Ruby. With Ruby he won at the European Championship at Azeitão to times gold and one silver medal and Diederik also won the world cup for Young Riders at Frankfurt. Also with the horses Vorst D, Davidoff and Ruby was Diederik successful at international competitions. Ruby ended at the 4^th place, good enough for the European Championship at Ermelo.

After his Junior/Young Rider period Diederik have been included with 2 horses in the A-cadre at the Future Test in 2010. He has driven a couple of beautiful competitions like Jumping Amsterdam, Aachen, Rotterdam and Den Bosch and won many prices.

In 2011 he won the 4^th place at the indoor championships in Ermelo with Ruby in the Grand Prix. At the Netherlands Championship at Outdoor Gelderland (De Steeg) he drove a couple times almost to the score of 70%. In the kür at music 73% and a 4^th place.

In the European Championships at Rotterdam in 2011 Diederik won with Ruby the Future Test and with Popeye in the U25 a 3th place and a 5^th place, also with scores from 70%.