The western lowland olingo is smaller than the northern olingo, but larger than the most montane member of the genus, the recently described olinguito ("little olingo"). While the Panamanian subspecies B. m. orinomus is about the same size as the eastern lowland olingo, the subspecies from west of the Andes, B. m. medius is smaller. The pelage is slightly lighter than that of the eastern species.
It has a head-body length of 31 to 41 centimetres (12 to 16 in), with a tail length of 35 to 52 centimetres (14 to 20 in). It weighs.9 to 1.2 kilograms (2.0 to 2.6 lb).