Alston's mouse opossum has a dull gray-brown back. The 2021 revision places the specimens and photographs it could confirm in Costa Rica's central highlands.
The back is dull gray-brown, while the fur between the facial markings and on the cheeks is paler. The dorsal fur is fluffy. The bare part of the tail is dark near its base and mostly whitish farther out.
In the Monteverde area, it was recorded at elevations with moist premontane forest. Another identified animal was photographed in secondary growth within cloud-forest country, and some specimens were taken near buildings.
An extinction-risk assessment has not been added yet.