Demodex gatoi sp. nov. is described in all its life stages from the domestic cat. The host was diagnosed with presumptive feline acquired immunodeficiency syndrome and harbored enormous numbers of both D. gatoi and D. cati Hirst, 1919. Unlike D. cati, which inhabits the hair follicles, D. gatoi resides on the epidermal surface. More than half of the D. gatoi population sampled was made up of ova indicating rapid population growth.