Orthorexia nervosa (Greek: ortho--correct, right; orexis--appetite, desire) is a term introduced in 1997 by the American doctor Steven Bratman and is defined as a pathological fixation with righteous and healthy eating. Clear classification criteria oforthorexia have not been developed yet and there has been an on-going discussion whether it belongs to the group of eating disorders or the obsessive-compulsive disorders.The aim of this paper is to summarise briefly the current state of knowledge regarding orthorexia and to point out the difficulties connected with an attempt to classify it in a given disorders group as well as with the attempt to establish the classification criteria.Despite the fact that the problem of orthorexia has been signalled in the Polish media, it has neither been discussed nor published in the Polish medical literature yet. Orthorexia starts when a diet becomes an escape from life--everyday activities are dominated by planning, buying and preparing "proper" meals. Each departure from this regime causes anxiety and guilty conscience and leads to even further tightening of the dietary habits. According to Bratmann, orthorexia is connected with an illusory feeling of safety (preventing from diseases), the urge to exercise a full control over one's life (elimination of the unpredictable), "a hidden conformism" (eating philosophy helps in a subconscious way to achieve a culturally accepted model of a beautiful body), a search for spirituality and identity, and a desire for self-deprivation.The arguments presented in this paper substantiate the expediency of implementing the epidemiological studies which will show the scale of the problem, its prevalence and conditionings. Data obtained in this way should facilitate the verification of classification criteria and will also help to formulate the diagnostic criteria of orthorexia.