The pygmy slow loris has a head and body length (measured from the top of the head to the base of the tail) of ; there is no significant difference in size between the sexes. The length of the skull is less than . The tail is short, averaging in length. The bodyweight ranges between , with an average mass of for males and for females. There are, however, large seasonal variations in bodyweight, and individuals up to have been recorded. The animal tends to have significantly higher bodyweights during the winter months, about 50 percent higher than the lowest values in the summer. The weight gains, achieved largely by increasing food intake, are triggered by changes in the length of the day and night. This seasonal change in bodyweight occurs in both sexes, in both pregnant and non-pregnant females—an adaptation thought to help ensure survival during winter when food resources become scarce. The species has distinctive teeth morphology: its third molar is triangular in outline and only slightly smaller than the first molar; its second molar is the largest. The incisors and canines on its lower jaw are procumbent (tilt forward) and together form a toothcomb that is used in grooming and feeding.