His personal best throw was 21.22 metres, achieved in June 1986 in Indianapolis. This is the current Norwegian record. 
Nilsen was tested for and found to be using banned substances in 1987 and 1992,  which led to a lifetime ban from organized sports. In 2004 he was pardoned and is free to participate in organized sports and competitions in any other sports than shot put. He may not participate in competitions which qualify for national or international championships.