The Assessment Questionnaire (GPAQ) is a questionnaire for patients to evaluate primary care in a number of key areas ranging from the access to care, the helpfulness of receptionists, the continuity of care, the doctors'communication skills, the patient's knowledge of self the General Practice care plans after consultation, and overall satisfaction. All questions can be calculated as a GPAQ score allowing services to be analysed, developed, and improved. The General Practice Assessment Questionnaire (GPAQ) was developed in the United Kingdom to evaluate the quality of general practice (i.e. primary care or family medicine). The aim of the present study was to translate and validate a Thai language version of GPAQ. Cross-sectional study: the content validity was examined by three experts in the Family Medicine field, and then the original GPAQ was translated into Thai with permission from the National Primary Care Research and Development Centre, University of Manchester and Safran. The translation process followed the guidelines for cross-cultural adaptation of self-report measures, including forward translation, synthesis of the translation, back translation, cross-cultural adaptation and pre-testing. The pilot study was done by distributing the questionnaire to a sample of 30 people before revision of the questionnaire. The reliability and validity of the translated version was then examined by distributing the questionnaire to 2,600 people visiting the out-patient clinic at the Department of Family Medicine, Ramathibodi Hospital in October, 2005. The response rate is about 70 percent. The results of the present study showed that the Thai version of GPAQ achieved good levels of reliability and validity, with the range of Cronbach's alpha coefficients being 0.7293-0.8324 in each aspect of GPAQ, namely access, doctor's communication skills, and patient enablement (understanding of self care after the consultation). However, a question about telephone consultations had to be excluded from the questionnaire to reach Cronbach's alpha coefficient of 0.8221. After translation and cross-cultural adaptation the Thai version of GPAQ can be used as a patient-administered instrument to evaluate the quality of primary care in Thailand.