Currently, there is debate in the eating disorders field regarding how to define atypical anorexia (AAN), how prevalent it is in community and clinical settings, and how AAN rates compare with low-weight AN. This systematic review assesses AAN literature from 2007 to 2020, to investigate: (a) the demographic characteristics of AAN studies, (b) the prevalence of AAN compared with AN, (c) the range of operational definitions of AAN and the implications of these definitions, and (d) the proportion of patients with AAN and AN represented in consecutive admission and referral samples.