In this work the structure of positronium hydride is established from analysis of electron, positron, and electron–positron pair density functions which are built from accurate Hylleraas-type wave function. In particular, analysis of the electron–positron pair density function shows that positronium hydride has not only an atomic structure with a positron added to a hydrogen negative ion, but also a diatomic molecular structure which consists of a hydrogen atom and a positronium.