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Background: Improvement in day-to-day functioning is a valued outcome of surgical intervention. A new functional status assessment instrument, the Activities Assessment Scale (AAS), was designed for a randomized clinical trial evaluating laparoscopic versus open hernia repair procedures. Study design: The study data set included 2,164 patients at baseline and 1,562 patients at 3-month followup. Only male patients were enrolled in the trial. The psychometric characteristics of the AAS were examined in statistical analyses of cross-sectional and longitudinal data from the trial. Correlational analyses, factor analyses, and t-tests were used to evaluate scale performance. Results: We found that the AAS was a reliable measure (Cronbach’s Coefficient Alpha =0.85) in the patient population studied. Factor analyses identified three subscales (sedentary activities; ambulatory activities; work and exercise activities). Construct validity was demonstrated by a correlation of 0.65 between the AAS and the physical functioning (PF) dimension of the SF-36 (p < 0.001); comparisons between clinical subgroups further confirmed its validity (p < 0.001). Patients reporting improvement on the physical functioning dimension after surgery showed an effect size of 1.20 for preoperative-postoperative change in their AAS scores. Conclusions: The AAS has been demonstrated to be a reliable, valid, and clinically responsive instrument that can be used to evaluate patient functioning after hernia surgery. It is easy to administer and requires less than 5 minutes of patient time to complete. This measurement system may prove useful in assessing surgical outcomes in both research and office practice settings. [Copyright &y& Elsevier]