Pigmentation polymorphism occurs in many mammals but is considered rare in natural populations. Here, we report the first record of pigmentation polymorphism in a Neotropical squirrel, Guerlinguetus ingrami, at a private reserve in southern Brazil. The number of records for leucistic squirrels was approximately half that for brown squirrels. We also tested the differences in activity patterns between the leucistic and the brown squirrels. Both phenotypes were diurnal, but there was temporal segregation between the two. Further studies are needed to elucidate the occurrence of leucism in G. ingrami, and the possible ecological and behavioral outcomes.