The Société Internationale de Chirurgie Orthopédique et de Traumatologie (SICOT), the Task Force on Outcome Studies of The American Academy of Orthopaedic Surgeons, and The Hip Society reached a consensus on the nomenclature to be used for the evaluation of the results of total hip arthroplasty. The Task Force of The American Academy of Orthopaedic Surgeons, to assess the results of total hip arthroplasty from the perspective of the patient, subsequently developed a questionnaire that incorporated this nomenclature. The validity and reliability data regarding this questionnaire are reported in this study. Twenty-five patients participated in the reliability test. The non-response rate was five (0.5 per cent) of 941 possible responses. Test-retest reliability was determined by calculating the Spearman correlation coefficients for each question. The coefficients ranged from 0.41 to 1.0 over a mean test-retest interval of sixteen days. Most items had Spearman coefficients that were greater than 0.50, indicating good or excellent reliability. Validity was assessed, for the fifty-four patients who participated, by calculating the Spearman correlation coefficients for the items regarding pain in the affected hip, limitation of usual activities, capacity for walking without support, and the Sickness Impact Profile. The coefficients ranged from 0.11 (pain and limitation of activity) to 0.56 (Sickness Impact Profile and limitation of activity). These coefficients reflected modest associations, as anticipated, indicating that pain, function, and health status are related yet distinct concepts.(ABSTRACT TRUNCATED AT 250 WORDS)