The majority of Gazans are registered as refugees
The population of the Gaza Strip increased by almost 40% between 1997 and 2007, according to the results of a Palestinian census.
The survey, taken before Israel's recent offensive, showed the territory has a population of 1.4 million people.
The Palestinian Central Bureau of Statistics estimated the annual growth rate at 3.3% and said the population would double in 21 years at that rate.
The UN estimates the world's current average population growth at 1.17%.
Aged under 15
Source Palestinian Central Bureau of Statistics website
In a statement, the West Bank-based bureau said: "Assuming a stable growth during the coming years, the Gaza Strip population will multiply [double] in 21 years."
There were mixed findings in the census for the people of Gaza.
The overwhelming majority of people in the territory (67.9%) continue to be UN-registered refugees. The figure was only slightly lower (65.1%) in 1997.
However, education and literacy showed signs of improvement.
The rate of people over the age of 10 unable to read fell from 11.3% in 1997 to 5.5% in 2007, as the proportion of those receiving school education rose from 62.8% to 70.6%.
Preliminary results from the census were released in February 2008.
According to those figures, the combined population of Gaza and the West Bank including east Jerusalem is 3.8 million.
The statistics bureau has not yet released final results on the West Bank or east Jerusalem.