Background The Edmonton Symptom Assessment Scale (ESAS), created by the Edmonton Group in 1991, is an instrument assessing symptom control commonly used in palliative care. It asks patients to rate nine items on an eleven-point numeric rating scales.

Objective The aim of this study was to translate the ESAS to Thai and validate its final version with transcultural adaptation for Thai palliative care patients. The original ESAS was translated into Thai with the Edmonton group`s permission. The translation process followed the cross-cultural adaptation of self-report measures` standard guidelines, including forward translation, synthesis of the translation, back translation, cross-cultural adaptation and pre-testing.

Methods This cross-sectional study was first undertaken with 44 end-stage cancer patients in the inpatient setting, which led to the final version. The reliability and validity of the final version, with a sample of 37 end-stage cancer patients, was then examined in the out-patient department at Ramathibodi hospital. The face validity was evaluated through patient interviews, using guide questions. The internal-consistency reliability was calculated by using SPSS program.

Results 91.8% of patients declared that the ESAS-Thai questionnaire was generally clear. It yielded a Cronbach's α of 0.7458 in the inpatient setting. After modifying the words ‘appetite’ and ‘well-being,’ 37 cancer patients, who were cared for by the Departments of Medicine, Surgery, Gynaecology and Otolaryngology, self-administered the questionnaire in the out-patient department. The mean age was 52.2 (10.8) with a 0.8904 Cronbach's α in the validation sample.

Conclusion After the translation and cross-cultural adaptation, the Thai version of the ESAS achieved good levels of face validity and internal-consistency reliability. It is now available as a patient-administered instrument to evaluate symptoms among palliative care patients in Thailand.