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OBJECTIVE To assess psychometric properties of the improved Work Disability Functional Assessment Battery (WD-FAB 2.0). DESIGN Longitudinal study. SETTING Community. PARTICIPANTS Three samples of working-age (21-66) adults (N=1006): (1) unable to work because of a physical condition (n=375); (2) unable to work because of a mental health condition (n=296); (3) general United States working age sample (n=335). INTERVENTION NA. MAIN OUTCOME MEASURES All samples completed the WD-FAB 2.0; the second administration came 5 days after the first. Construct validity was examined by convergent and divergent correlational analysis using legacy measures. Test-retest reliability was assessed by intraclass correlation coefficients (ICC3,1). Standard error of the mean (SEM) and minimal detectable change (MDC90) were calculated to measure scale precision and sensitivity. RESULTS Physical function ICCs ranged from 0.69 to 0.77 in the general sample, and 0.66 to 0.86 in the disability sample. Mental health function scales ICCs ranged from 0.62 to 0.73 in the general sample, and 0.74 to 0.76 in the disability sample. SEMs for all scales indicated good discrimination; those for the physical function scales were generally lower than those for the mental health scales. MDC90 values ranged from 3.41 to 10.55. Correlations between all WD-FAB 2.0 scales and legacy measures were in the expected direction. CONCLUSIONS The study provides substantial support for the reliability and construct validity of the WD-FAB 2.0 among 3 diverse samples. Although initially developed for use within the Social Security Administration (SSA), these results suggest that the WD-FAB 2.0 could be used for assessment and measurement of work-related physical and mental health function in other contexts as well.