WASHINGTON (MarketWatch) - The U.S. recession that started in December 2007 ended in June 2009, according to the group charged with determining when recessions officially begin and end. The National Bureau of Economic Research said the economy bottomed out in June 2009, followed thereafter by a slow expansion. The group said the 18-month recession was the longest since the end of World War Two. If another downturn occurs in the near future, the NBER said, it would constitute a separate recession. The NBER said its determination of the recession's end does not mean the U.S. is now healthy. "In determining that a trough occurred in June 2009, the committee did not conclude that economic conditions since that month have been favorable or that the economy has returned to operating at normal capacity, NBER said. "Rather, the committee determined only that the recession ended and a recovery began in that month."