The virus is thought to contain 2 identical copes of a positive sense (i.e., mRNA) single-stranded RNA strand about 9,500 nucleotides long. These may be linked to each other to form a genomic RNA dimer.

The RNA dimer is in turn associated with a basic nucleocapsid (NC) protein. This nucleoprotein filament may be helical, although this has not been determined yet in HIV.

The ribonucleoprotein particle is encapsidated by a capsid made up of a capsid protein (CA), p24. The capsid environment also contains other viral proteins such as integrase and reverse transcriptase. It also contains a wide variety of other macromolecules derived from the cell including tRNAlys3, which serves as a primer for reverse transcription. The capsid has an icosahedral structure.

The capsid is in turn encapsidated by a layer of matrix protein (MA) associated with a lipid bilayer or envelope. The matrix protein may be: a continuous shell attached to the envelope as in HIV noncontinuous but associated with envelope separate from the envelope.