The infection of humans by human immunodeficiency virus type 1 is characterized by a prolonged stage of clinical quiescence. This clinically asymptomatic period may be based, in part, on the development of cell populations within the body that maintain human immunodeficiency virus type 1 in a state of latency. Recent advances in the understanding of the molecular mechanisms involved in various forms of cellular latency of human immunodeficiency virus type 1 have begun to shed light on the variable period of asymptomatic infection. The elucidation of cellular retroviral latency, in vivo, will also be critical to the design of novel therapeutic approaches with which to combat human immunodeficiency virus type 1 infections.