It is generally accepted that HIV infection is a necessary precondition for the development of AIDS.

The immune system can be compromised in other ways, and in rare cases this can lead to the same kinds of infection as those seen in AIDS. This is called idiopathic CD4 lymphocytopenia or ICL. The immune suppression seen in ICL is not always the same as in AIDS however, often clearing up without treatment.

HIV's exact role in the development of AIDS is unknown, but it is certainly a central one. The immune system is immensely complex and there are many ways in which it can be affected by a retrovirus such as HIV. It is not clear what role other factors might play as well.