It makes the most sense to control disease as early as possible.
The number of people receiving medicines for the AIDS virus leapt by a quarter last year but more patients need to be brought into treatment before they are too sick, the World Health Organisation said on Monday.
Presenting the data at an international conference on AIDS in Vienna, the WHO said an estimated 5.2 million people were being treated for the AIDS virus at the end of 2009 after an extra 1.2 million people started treatment during the year.
Earlier HIV treatment can prevent so-called "opportunistic infections" including tuberculosis (TB), which is the biggest killer of people with HIV.
The WHO says deaths from TB could be reduced by as much as 90 percent if people with both HIV and TB started treatment earlier, when their immune systems have not been weakened too much by the virus.
Early treatment key for HIV-positive patients: WHO