AIM: To propose a diagnostic proceeding and to try to verify the prevalence of orthorexia nervosa (ON), an eating disorder defined as "a maniacal obsession for healthy foods". MATERIALS AND METHODS: 404 subjects were enrolled. Diagnosis of ON was based on both the presence of a disorder with obsessive-compulsive personality features and an exaggerated healthy eating behaviour pattern. RESULTS: Of the 404 subjects examined, 28 were found to suffer from ON (prevalence of 6.9%). The analysis of the physiological characteristics, the social-cultural and the psychological behaviour that characterises subjects suffering from ON shows a higher prevalence in men and in those with a lower level of education. The orthorexic subjects attribute characteristics that show their specific "feelings" towards food ("dangerous" to describe a conserved product, "artificial" for industrially produced products, "healthy" for biological produce) and demonstrate a strong or uncontrollable desire to eat when feeling nervous, excited, happy or guilty.