Within 2 to 4 weeks after infection with HIV, some people may have flu-like symptoms, such as fever, chills, or rash. The symptoms may last for a few days to several weeks. Other possible symptoms of HIV include night sweats, muscle aches, sore throat, fatigue, swollen lymph nodes, and mouth ulcers. Having these symptoms does not mean you have HIV. Other illnesses can cause the same symptoms. Some people may not feel sick during early HIV infection (called acute HIV). During this earliest stage of HIV infection, the virus multiplies rapidly. After the initial stage of infection, HIV continues to multiply but at lower levels.

More severe symptoms of HIV infection for persons not on ART may not appear for many years until HIV has developed into AIDS. People with AIDS have weakened immune systems that make them prone to opportunistic infections. Opportunistic infections are infections and infection-related cancers that occur more frequently or are more severe in people with weakened immune systems than in people with healthy immune systems.

Without treatment, HIV transmission is possible at any stage of HIV infection—even if a person with HIV has no symptoms of HIV.