Disability questionnaires are increasingly used for clinical assessment, outcome measurement of treatment and research methodology of low back pain. Their use in different countries and cultural groups must follow certain guidelines for translation and cross-cultural adaptation. The translation of such an instrument must be tested for its reliability and validity to be applied and to allow comparability of data. The Oswestry Disability Index and the Roland-Morris Disability Questionnaire are two disability questionnaires most commonly used as outcome measures in patients with low back pain. The two questionnaires were translated for use with the Greek population, were back translated and tested, and became available in a final version. The Greek versions of the Oswestry Disability Index and the Roland-Morris Disability Questionnaire were tested in 697 patients with low back pain. Internal consistency reliability for the Greek translation of the Oswestry Disability Index and the Roland-Morris Disability Questionnaire reached a Cronbach's alpha coefficient of 0.833 and 0.885 respectively. Face validity and content validity were ensured. Concurrent validity was assessed using a six-point pain scale as a criterion. The correlation of both scales was significant. The Greek translation of these disability questionnaires provided reliable and valid instruments for the evaluation of Greek-speaking patients with low back pain.