Background/Aim: As Thai people living with HIV/AIDS gain increasing access to antiretroviral (ARV) therapy,it is important to evaluate the impact this has not only on clinical outcomes, but also on patients’functional status and well-being. In this study, we translated, culturally adapted and tested the reliabilityand validity of two widely-used health-related quality of life questionnaires – the MOS-HIV Health Surveyand the SF-12 – in people living with HIV/AIDS in Northern Thailand. Methods: Questionnaires wereadministered to 100 patients at community hospital outpatient ARV clinics in northern Thailand. Reliabilitywas estimated using Cronbach’s alpha, while evidence for validity was tested using known-groupscomparison based on CD4 group, symptom distress score, bed days and days of reduced activity in the pastthree months. Results: Patients’ median age was 36, with 58% female, 58% working as laborers, and 60%completing at least primary education. Median CD4 count was 218 cells/mm3. There were no missing data.For the MOS-HIV and SF-12, mean physical summary scores were 53.1 and 49.0 respectively; mean mentalsummary scores were 53.4 and 45.6, respectively. Internal consistency coefficients were >0.7 for all butone scale, the PF scale (0.67). As hypothesized, scores were slightly to moderately correlated with CD4count, symptom score, number of days in bed or with reduced activity. Correlations were higher withphysical health scores than with mental health scales. The MOS-HIV discriminated clinical known groupsslightly better than the SF-12. Conclusion: Both the MOS-HIV and the shorter SF-12 were successfullyadapted for people with HIV/AIDS in Northern Thailand, and showed encouraging evidence for reliabilityand validity. These patient reported questionnaires could be valuable tools in evaluating therapeuticinterventions and other innovations in health and social services, and to estimate health needs andpopulation disability related to HIV.