The former army colonel seized power in a coup in 1994, and has remained in office through several flawed elections since. No one expected he would be turned out this time in a vote condemned as unfair by the body of regional leaders called the Economic Community of West African States (ECOWAS).
ECOWAS declined to even send observers, saying a free vote was impossible because of a high level of intimidation and fear, and Jammeh's dominance of the media.
ECOWAS, consisting of 15 West African states, reported "an unacceptable level of control of the electronic media by the party in power ... and an opposition and electorate cowed by repression and intimidation."
Gambia's voting method hearkens back to its days as a British colony: Voters place a marble into the drum of their chosen candidate within a polling booth, a method used because many voters are illiterate. (In other West African countries with high illiteracy rates, photographs are published on ballot papers.)
There was a heavy military presence on the streets in the capital, Banjul, on voting day, which opposition presidential candidate Ousainou Darboe said was intended as an intimidation tactic.
Gambia is Africa's smallest country just 30 miles wide, with 1.7 million people: a sliver of land on either side of the Gambia River, surrounded by Senegal, except for its small Atlantic coastline.
The country's main income derives from its port, tourism and agriculture. Around two-thirds of the population live on less than $1.25 a day, and a similar proportion live in villages.
In 2007 Jammeh was widely condemned internationally for his boast that he had invented a cure for AIDS, smearing patients with a green herbal paste and ordering them to stop taking anti-retroviral medication so that his remedy could take effect.
He was also criticized in 2008 for his declaration that homosexuals must leave the country, and his threat to behead those who remained. In the last election. five years ago, he said he would only develop regions that voted for him, "but if you don't vote for me, don't expect anything."
Jammeh voted Thursday wearing his traditional white flowing gowns, and dismissed criticisms of his government, which human rights groups accuse of killing or detaining journalists, activists and regime opponents.
"No Western country can tell me anything about democracy. In this country we fear only God and I don't care what anybody says. What matters to me is the development of this country. Africa has been insulted for centuries and this is unacceptable," he told reporters at the polling station.
He also dismissed the ECOWAS criticism of the vote.
"I will never compromise peace and stability at the altar of so-called democracy," Jammeh said, according to agencies.
"Do I look like a loser? There is no way that I can lose unless you tell me that Gambians are mad," Agence France-Presse quoted him saying.
-- Robyn Dixon