Röthlin has set four Swiss national records at the marathon distance: In September 2001 at the Berlin Marathon, his time of 2:10:54 eclipsed the previous Swiss national record of 2:11:10 (set by Daniel Boltz in 1991). In April 2004, in his victory at the Zürich Marathon, Röthlin lowered the national record to 2:09:56. In April 2007, he lowered the national record again, when he won the Zürich Marathon in a time of 2:08:20, and in February 2008, he once more improved the Swiss record to 2:07:23 when he won the Tokyo Marathon.
Röthlin attempted no marathons in 2009, because he contracted thrombosis during a flight from the United Arab Emirates in the Spring of 2009, which led to a pulmonary embolism and fluid buildup in his chest; the condition was treated with rest and medication.
At the 2012 Tokyo Marathon he had his fastest performance since his victory in 2008, as he finished fifth with a time of 2:08:32 hours.