His first event was the 10,000m. Midway through the race, Viren was running in fifth place when he suddenly stumbled and fell. He rose quickly and moved up to second place within 230 metres. The lead changed hands several times. Then with 1½ laps to go, Viren applied pressure. One by one, his opponents fell behind. Lasse won by six metres and broke the seven-year-old world record. Ten days later, in the 5,000m final, Viren fought off the challenge of Mohamed Gammoudi of Tunisia to complete the long distance track double.
At the 1976 Olympic Games in Montréal, Viren had an easier time in the 10,000m. Carlos Lopes led for most of the race. Lasse passed him 450 metres from the finish and won by 30 metres. The 5,000m was harder. Although the Finnish athlete was in the lead at the beginning of the last lap, only five metres separated the first six runners. Coming out of the final turn, Viren beat back a fierce challenge by New Zealand's Dick Quax and won his fourth gold medal.
Viren is the only repeat winner of the 5,000m. He returned to the Olympic Games in 1980, placing fifth in the 10,000m and, indisposed by an intestinal ailment, dropping out of the marathon. Lasse Viren was a strong supporter of training in the woods. "The tranquillity of nature creates mental strength" he said. "When you run in the woods, you will have to change rhythm to avoid roots, just in the same way as you have to be constantly alert in a competition".