Leo Pusa, 56, a three times former champion took back the title won by a fellow Finn last year, spending almost 12 minutes in the 110 degrees Celsius (230 degrees Fahrenheit) heat.
Natalya Tryfanava from Belarus held onto the title she won last year in the women's contest, managing to stick it out for just over eight minutes.
Ninety competitors from 12 countries took part in the contest, held for the sixth time in the small Finnish town Heinola, some 130 kilometers (80 miles) north of the capital Helsinki.
Competitors sat in sauna cabins set up on a stage for as long as they could take the heat before running out to cool down.
Water was poured onto the sauna stove every 30 seconds to keep the temperature up.
A crowd of several thousand followed their favorites on a big video screen, cheering on every competitor as they rushed out.
"In the sauna, my head was almost empty, no thoughts about victory or anything," said 36-year-old Tryfanava, her face and limbs red from the heat.
"I was just trying to relax as much as possible, keep my breathing in check and not get burned, and still enjoy it."
Tryfanava said she and her team mates, who came third and fourth, underwent a special training program, but declined to reveal details.
The men's contest has always been won by a Finn.
Pusa said it would be hard for foreigners to beat Finns as saunas are the country's favorite pastime.
Finland has more than 2 million saunas for a population of 5 million.
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