The US economy emerged from recession in June last year after an 18-month downturn, according to the country's National Bureau of Economic Research.
'The recession lasted 18 months, which makes it the longest of any recession since World War II,' the NBER said.
Unlike many other countries - where a recession is defined as two consecutive quarters of shrinking economic output - in the United States the existence of a recession is determined by a seven-member NBER panel.
More than eight million jobs were lost in the slump that was triggered by dodgy Wall Street mortgage investments.
Although the economic pain continues to be felt across the country, with one in ten US workers still without a job, the NBER said economic data showed the worst had now passed.
Despite economists' warnings of a double-dip recession, the bureau said the economy had recovered enough to say that any new slide would constitute a new recession.
'The committee decided that any future downturn of the economy would be a new recession and not a continuation of the recession that began in December 2007,' it said.
At the same time it warned that 'economic activity is typically below normal in the early stages of an expansion, and it sometimes remains so well into the expansion'.
Although the depth of the crisis had already been clear, the NBER confirmed it was longer that those which began in 1973 and 1981 and which both lasted 16 months.
