Within Nesomyinae, it is most closely related to the genus Eliurus, and DNA sequence data suggest that the current definitions of these two genera need to be changed.

In Voalavo, there are two glands on the chest (absent in Eliurus) that produce a sweet-smelling musk in breeding males.

[2] A second species, eastern voalavo, was named by Goodman and colleagues in 2005 from the region of Anjozorobe in the Central Highlands.

[3] The two Voalavo species are closely related and quite similar, but differ in various subtle morphological characters (mainly measurements) and by 10% in the sequence of the mitochondrial gene cytochrome b.

Before the discoveries of Monticolomys (published in 1996) and Voalavo (1998), all of the known genera within Nesomyinae were quite distinct from each other, so much so that phylogenetic relationships among them long remained obscure.

Like Monticolomys (closely related to Macrotarsomys), however, Voalavo shows clear similarities to another nesomyine genus, Eliurus.

[8] Molecular phylogenetic analysis of nuclear DNA supports a close relationship between Eliurus, Voalavo, and two other nesomyine genera, Gymnuromys and Brachytarsomys.

Relative tail length in northern voalavo (136% of head and body length) is comparable to that of the longest-tailed species of Eliurus, Grandidier's tufted-tailed rat and Petter's tufted-tailed rat,[2] but V. antsahabensis has a somewhat shorter tail.

[14] Unlike all other nesomyines but Brachyuromys, Voalavo lacks an entepicondylar foramen, an opening on the humerus (upper forelimb bone).

The tegmen tympani, the roof of the tympanic cavity, is much reduced in Voalavo relative to Eliurus.

The subsquamosal fenestrae, openings in the squamosal bone at the back of the skull, are larger in Voalavo than in Eliurus.

[19] Like Eliurus, Voalavo has moderately high-crowned (hypsodont) molars[20] with crowns that consist not of discrete cusps, but of transverse laminae (plates) that generally lack longitudinal connections.