Around 96,000 people have the virus, including 4315 who have been diagnosed in Scotland.
While the available treatments are said to be working well, health officials are concerned that many people are unaware they have been infected. They estimate around 25% of people with HIV do not know they have it.
A report by Health Protection Scotland said: "There is evidence that individuals are being diagnosed at a late or very late stage of infection when treatment may be less effective."
HIV attacks the immune system and reduces the ability to fight infections. About 95% of patients catch it through sexual contact.