OBJECTIVES: The aim of this study was to test the unidimensionality of 65 items from nine widely used pain questionnaires in preparation for computerized adaptive pain assessment. METHODS: Random samples of adults were contacted on the internet (N=782) and telephone (N=750). 65 items were selected mainly from Brief Pain Inventory, MOS Pain Measures, Oswestry Low Back Pain Disability Questionnaire, NottingHam Health Profile, McGill Pain Questionnaire, Health Disability Index, Migraine-Specific Questionnaire, Aberdeen Back Pain Scale, and Headache Impact Test. Mplus software was used to perform confirmatory and exploratory factor analyses of polychoric correlations among the items. Model was examined through eigenvalue analysis, interfactor correlations, and root mean square residuals. RESULTS: Confirmatory factor loadings ranged from 0.53 to 0.92 with 90% of them higher than 0.7. Three factors were rotated to an oblique solution. Examination of exploratory factor analysis revealed two subdimensions of pain based upon item content: pain severity and pain impact. The third dimension observed in the three-factor solution, interpreted as current pain, was defined by questions without recall period. Eigenvalue analyses showed that the first factor explained more than 65 percent of the total variance in all pain item scores. Three factors explained 74% of the variance. The interfactor correlations were high, ranged from 0.64 to 0.67. Root mean square residuals were low, 0.07 for one-factor solution and 0.05, 0.03 for two- and three-factor solution respectively. CONCLUSION: Most items from widely used questionnaires measure one single underlying construct of pain sufficiently to meet the assumption of Item Response Theory. Items selected will be calibrated on a standard metric to estimate scores at patient’s specific pain level. Further investigation on the application of IRT methods and computer technology in pain assessment is warranted.