Most of those affected are from rural areas
Some 380,000 Colombians were forced from their homes last year by the continuing armed conflict, a local human rights group has said.
The Centre for Human Rights and the Displaced, Codhes, says this is a 25% rise on 2008 and brings the total displaced since 1985 to 4.6 million.
Government officials say the number registered as displaced has risen.
But they say the Codhes total includes figures from previous years and those falsely claiming compensation.
In its annual report, Codhes says 2008 saw the rate of displacement rising to levels last seen in 2002, the worst year on record when 410,000 people were forced to flee.
According to its study, 380,863 people had to leave their homes or places of work as a result of the armed conflict between guerrillas, paramilitary groups and the security forces.
Codhes says that between 1985 and 2008, 4.6 million Colombians have been uprooted.
"The great majority live in severe conditions of poverty," the Codhes report said, while their own land and property had fallen into the hands of others in a "de facto expropriation".
According to government figures, 2.9 million people were displaced between 1997 and 2008.
The government department dedicated to helping such people, Accion Social, said the number seeking to be registered as displaced and therefore qualifying for aid had risen, but often these were for events dating back to the 1980s, 1970s and even 1961.
Accion Social said around a third of the people included in the Codhes figure had in fact been displaced in 2007.
Fraudsters, officials said, had also mounted schemes to register thousands of people as displaced thereby "robbing those really displaced by violence in Colombia of the chance to get help".
Whatever the actual figures, it is clear that two Colombias are developing under President Alvaro Uribe, says the BBC's Jeremy McDermott in Medellin.
Towns and cities, where the majority of Colombians live, have become safer under his administration, with murders and kidnappings down.
But in rural areas, where most of the displacement takes place, the situation is as bad, or perhaps worse, than ever, our correspondent says.