The number of over-50s infected with HIV has more than doubled in seven years, according to new research.
In 2000, just 299 new cases were recorded in England, Wales and Northern Ireland, the Health Protection Agency said.
However, this figure jumped to 710 in 2007, according to the body.
Among younger age groups, a third have the HIV infection identified at a similar level of progression.
During the study period, three-quarters of deaths among HIV-infected people aged 50 and over occurred within a year of diagnosis.
Compared with younger adults carrying the virus, older people were significantly more likely to have been infected through sex with men.
Older "straight" adults were more likely to acquire the virus in the UK, but there was evidence of white heterosexual men picking up the infection abroad.
Ruth Smith, a senior HIV scientist at the Health Protection Agency's Centre for Infections, said: "We must continually reinforce the safe sex message - using a condom with all new or casual partners is the surest way to ensure people do not become infected with a serious sexually transmitted infection such as HIV."
The findings are published online in the journal AIDS and were presented at the International Aids Conference in Vienna.