HIV superinfection is a condition in which a person with established human immunodeficiency virus infection acquires a second strain of the virus. The second strain co-exists with the first and may cause more rapid disease progression or carry resistance to medicines.

As of 2005 there were 16 cases reported in the worldwide literature, though given the high cost and relative rarity of phylogenetic screening, this number may not reflect the entire population of superinfected individuals. People with HIV risk superinfection by the same actions that would place a non-infected person at risk of acquiring HIV. These include sharing needles and forgoing condoms with HIV-positive sexual partners.