It said 56,000 people had become infected with the virus that causes AIDS in 2006
whereas previous estimates put the figure at only 40,000.
However, the CDC said it was not as if there was any alarming increase in infections, but simply better detection methods had been devised.
For instance, new blood tests could tell how recently an HIV infection occurred, allowing researchers to pinpoint the year it happened. Also new statistical methods could be more accurate.
Whatever the case, the fact remained the epidemic was worse than previously estimated, the CDC conceded.
The group added that the annual number of new infections was never as low as 40,000, and that it has been roughly stable since the late 1990s.
The CDC described the findings as a "wake-up call that the US HIV/Aids epidemic is far from over".
"The new estimates underscore the need to expand access to HIV prevention to gay and bisexual men, especially younger men, and to expand access to African-American men and women as well," Richard Wolitski, PhD, acting director of the CDC's division of HIV/AIDS Prevention said.
The revised estimated and the methodology behind it are due to be presented at the opening of an international Aids conference in Mexico City on Sunday.
Ahead of the meeting, thousands of activists marched through the city to protest at discrimination against people with HIV.