Dennis competed in three Paralympics for the United States winning a toal of 10 medals including four gold. At his first games in 1988 he won the 100m, 200m and 400m all in new world records, he also helped the United States team to win the bronze medal in the 4 × 100 m. At the 1992 Summer Paralympics Dennis didn't compete in the 400m and was unable to defend his titles in the 100m and 200m finishing second and third respectively he did however win a gold medal in the long jump in a new world record, he also won silver in the pentathlon and as part of the United States 4 × 100 m relay team. His third games came in his home country for the 1996 Summer Paralympics where he competed in the 100m and long jump and won a bronze medal in the 4 × 100 m.