HOOS was developed as an extension of the Western Ontario and McMaster Universities' Osteoarthritis Index questionnaire for measuring symptoms and functional limitations related to the hip(s) of patients with osteoarthritis. To determine the validity and reliability of the Thai version of the Hip disability and Osteoarthritis Outcome Score (HOOS) vis-à-vis hip osteoarthritis, the original HOOS was translated into a Thai version of HOOS, according to international recommendations. Patients with hip osteoarthritis (n = 57; 25 males) were asked to complete the Thai version of HOOS twice: once then again after a 3-week interval. The test-retest reliability was analyzed using the intraclass correlation coefficient (ICC). Internal consistencies were analyzed using Cronbach's alpha, while the construct validity was tested by comparing the Thai HOOS with the Thai modified SF-36 and calculating the Spearman's rank correlation coefficients. The Thai HOOS produced good reliability (i.e., the ICC was greater than 0.9 in all five subscales). All of the Cronbach's alpha showed that the Thai HOOS had high internal consistency (Cronbach's alpha greater than 0.8), especially for the pain and ADL subscales (0.89 and 0.90, respectively). The Spearman's rank correlation for all five subscales of the Thai HOOS had moderate correlation with the Bodily Pain subscale of the Thai SF-36. The pain subscale of the Thai HOOS had a high correlation with the Vitality and Social Function subscales of the Thai SF-36 (r = 0.55 and 0.54)-with which the symptom subscale had a moderate correlation. The Thai version of HOOS had excellent internal consistency, excellent test-retest reliability, and good construct validity. It can be used as a reliable tool for assessing quality of life for patients with hip osteoarthritis in Thailand.