The aim of the study was to define orthorexia nervosa (ON) based on the latest scientific findings regarding incidence, groups and risk factors as well as relationships between ON and other clinical entities. The paper is based on the review of the MEDLINE/PubMed databases. Publications published between 2009 and 2019 were analyzed in terms of epidemiology, risk factors and formulation of the ON concept. ON is a clinical entity of an unclear origin and various authors have continued their discussion on the relation between ON and other groups of disorders (AN, BN, OCD, ASD). Epidemiological data vary and depending on a population present extreme values from anywhere between 1% and 90%. Risk factors are alternatively identified in various groups and authors are not unanimous as for the effect of determinants such as anthropometric and sociodemographic variables on the presence of ON symptoms. Presented findings are affected by the fact that there is a relatively small number of studied groups, they are not fully representative and applied tools are different: BOT, ORTO-15, EHQ, DOS. Since the nosological status of ON remains unclear and there are no standard and operationalized diagnostic criteria and reliable assessment tools, ON requires further study. Similarly, because it is still not known how to best treat ON – which is caused by ambiguities in the concept of the phenomenon itself – prevention and therapy programs, which are non-existent, should be developed (in risk groups in particular).