HIV-1 infection is generally characterized by a long-term, chronic disease course gradually progressing to AIDS. However, there are a few but strikingly different scenarios. A small fraction of HIV-1 infections remains normal both clinically and immunologically over 10 years or more after seroconversion. Conversely, another marked fraction is featured by an extremely rapid disease progression taking place even within one year. Determining the host factors of these different disease courses would be extremely helpful for better understanding and control of AIDS. Here we show examples of host genetic polymorphisms, which can affect HIV-1 transmission and disease courses.