The Croatian part of the race was taking place in the coastal city of Zadar, where 4,000 runners gathered at the ancient Roman Forum and started the run towards Primosten, about 80 kilometres along the coast to the south.
The global race began at all designated locations at the same time, in Croatia at 1pm local time.
The race has no start or finish line or the distance that needs to be covered, and the winner is the person who runs the longest. Runners are followed by a catcher car, which starts 30 minutes later, and the last person to be overtaken by the car will be the winner.
The purpose of the race is to raise funds for the Wings for Life Foundation whose mission is to find a cure for spinal cord injury.
The ambassador of the Croatian race, Mario Valentic, said his aim was to have fun, run as long as he could and then take a swim in the sea. "I've come to participate, to run as long as I can. We know the purpose of the race and that's the only motive," he said.
Zadar mayor Bozidar Kalmeta also took part in the race. He said he we was proud of the 4,000 people who had decided to help by running in the race.
Manda Knezevic, head of the Croatian Association of Tetraplegics and Paraplegics, said that people had recognised their problem. "The more funds for research are raised, the better. This race has raised public awareness both in Croatia and globally," she said, adding that she would try to cover five kilometres.