Tehran was lit up on the eve of the birthday of the 12th Imam, sometimes known as the Mehdi. He is said to have gone into hiding in the 10th Century but is expected to return.
Huge crowds headed for Jamkaran mosque - said to have been visited by the Imam - to mark his birthday, waving flags and chanting: "Ya Mehdi".
On Saturday, the Imam's birthday, worshippers wrote their desires on pieces of paper and sent them to the Imam by putting them down a sacred well.
Throughout Iran people celebrated with banners, flags and colourful lights. This man's flag says: "Mehdi - the world is awaiting you".
Among them were two women walking past a huge religious cloth banner in Tehran.
A birthday cake for the Imam at a street festival in Tehran's biggest square, Azadi Square. This year, many carried Hezbollah flags after the recent fighting in Lebanon.
People were asked to bring flowers to Azadi square. Later the flowers were to be taken by helicopter and strewn from the air over the Jamkaran mosque.
The owner of this shop distributed sweets and soft drinks to passers-by on the eve of the birthday of the Imam. This is common throughout the country.
President Mahmoud Ahmadinejad spoke on the doctrine of the 12th Imam at an international conference in Tehran. Pictures by Mohsen Shandiz