Purpose The present study aimed to validate the ORTO-15 questionnaire for orthorexia nervosa (ON), translated by our group into the Greek language, and replicate the findings of the recently proposed 6-item ORTO-R. Methods The tool was translated into the Greek language (ORTO-15-GR) using the forward–backward–forward method. A total of 848 adults participated in the validation study by filling in the questionnaires and providing general characteristics (age, gender, educational level, body weight, and height). The internal consistency of the tool was assessed by the omega (ω) coefficient, and confirmatory factor analyses (CFA) examined its factorial structure. Using the original six items of the ORTO-15 tool, a separate CFA model examined the factorial structure of the proposed ORTO-R tool. Furthermore, regression models tested the association of ORTO-R with study variables. Results For ORTO-15-GR, the omega coefficient was 0.70 and for the ORTO-R 0.65. For the latter, the CFA revealed acceptable goodness-of-fit (standardized factor loadings from 0.36 to 0.64); however, all ORTO-15 models were characterized by a poor fit. In addition, there was a negative association between ORTO-R score and female gender, body mass index (BMI), and having a nutrition-related health problem. Conclusion The replication of ORTO-R indicates that it is a reliable tool in the field of ON. Therefore, the use of a 6-item questionnaire for ON assessment appears promising in research and clinical settings. Supplementary Information The online version contains supplementary material available at 10.1007/s42000-022-00351-4.