AIM: To validate a questionnaire for the diagnosis of orhorexia oervosa, an eating disorder defined as "maniacal obsession for healthy food". MATERIALS AND METHODS: 525 subjects were enrolled. Then they were randomized into two samples (sample of 404 subjects for the construction of the test for the diagnosis of orthorexia ORTO-15; sample of 121 subjects for the validation of the test). The ORTO-15 questionnaire, validated for the diagnosis of orthorexia, is made-up of 15 multiple-choice items. RESULTS AND CONCLUSION: The test we proposed for the diagnosis of orthorexia (ORTO 15) showed a good predictive capability at a threshold value of 40 (efficacy 73.8%, sensitivity 55.6% and specificity 75.8%) also on verification with a control sample. However, it has a limit in identifying the obsessive disorder. For this reason we maintain that further investigation is necessary and that new questions useful for the evaluation of the obsessive-compulsive behavior should be added to the ORTO-15 questionnaire.