Voting in Iran was extended for several hours because of the crowds.
In the week's leading up to election day, Iran's highly controversial President Mahmoud Ahmedinejad has been fighting for his political life.
The state media has already declared him the winner, but one of his challengers --Hossein Mousavi-- also claims victory.
Click play for more analysis with CBN News' Gary Lane.
Election results could take a while to be counted, and President Obama says he's closely watching.
Behind the Election
Three candidates are opposing incumbent Mahmoud Ahmadinejad and the future stability of the Middle East is hanging in the balance.
The campaign leading up to Iran's presidential election surprisingly resembled an American political campaign.
There were posters, banners and mass rallies with supporters and a first on Iranian state television, a series of presidential debates, and even candidate websites.
But the government has put a block on Facebook the social network popular with Iranian youth.
Top reformist candidate Hossein Mousavi is popular with young voters. He views the Internet and Facebook as an important tool for attracting more of them to his campaign.
A Mousavi supporter suggests the government is working against his candidate.
"In the past they used to say we block sites that have immoral information but now they seem to be overdoing it by filtering websites that are not in line with their political party," he said.
Women Play Large Role
Also surprising for an Iranian presidential election is the prominent role of women.
Zahra Rahnavard, wife of former prime minister Mousavi has been an outspoken supporter of reform on the campaign trail.
"An atmosphere of freedom of speech, press and thought is absent," she said. "We feel that we do not possess an independent and great economy because of the wrong policies and adventurist behavior."
A Vote for the Economy
While President Ahmadinejad has focused his attention against Israel and the pursuit of nuclear technology, the Iranian economy has worsened. The people now suffer from an unemployment rate of at least 12.5 percent and inflation is hovering near 20 percent.
President Ahmadinejad has tried to keep the focus on issues of corruption and political mudslinging. At this rally he lashed out at his opponents.
"We have prepared our throats for your lances and swords. We will not accept abjectness," he said.
Conservative candidate Mohsen Rezaei, the former chief of Iran's revolutionary guards says he is campaigning against an elite government that is out of touch with the daily struggles of the people.
"The price of people's daily needs has increased twofold while the incomes have not been increased over the past four years," Rezaei said.
So, while the Iranian presidential campaign resembles an American one it is perhaps not foreign policy issues that will determine the outcome of this election.
Like the Americans last November, Iranian voters this time around may likely say, "It's all about the economy."