Acquired immune deficiency syndrome (AIDS) was first reported in women in 1981 and by 1990 had become the sixth leading cause of death in 25 to 44 year old women in the United States. By 1999 women accounted for 23% of all new AIDS diagnoses and 32% of newly reported HIV diagnoses. By 1995, heterosexual transmission surpassed injection drug use as the most common mode of transmission in women.