It is easy to think of the PSP as a failure when comparing it to the monstrous success of the Nintendo DS, but with 50 million is no small feat to accomplish. A territory only Nintendo has been able to enter in the handheld market. The press release from Sony reads: "the cumulative worldwide sell-in units of PSP handheld entertainment system (PSP-1000, 2000 and 3000 series) reached a total of 50 million units as of January 2009". Basically that 50 million units had been sold to stores around the world through January.
The PSP first launched in December 2004 in Japan, followed by a North American launch in March 2005 and Europe/PAL territories in September 2005.