Objective: The authors developed and evaluated a rating scale, the Attitudes toward Handheld Decision Support Software Scale (H-DSS), to assess physician attitudes about handheld decision support systems. Design: The authors conducted a prospective assessment of psychometric characteristics of the H-DSS including reliability, validity, and responsiveness. Participants were 82 Internal Medicine residents. A higher score on each of the 14 five-point Likert scale items reflected a more positive attitude about handheld DSS. The H-DSS score is the mean across the fourteen items. Attitudes toward the use of the handheld DSS were assessed prior to and six months after receiving the handheld device. Statistics: Cronbach's Alpha was used to assess internal consistency reliability. Pearson correlations were used to estimate and detect significant associations between scale scores and other measures (validity). Paired sample t-tests were used to test for changes in the mean attitude scale score (responsiveness) and for differences between groups. Results: Internal consistency reliability for the scale was α = 0.73. In testing validity, moderate correlations were noted between the attitude scale scores and self-reported Personal Digital Assistant (PDA) usage in the hospital (correlation coefficient = 0.55) and clinic (0.48), p < 0.05 for both. The scale was responsive, in that it detected the expected increase in scores between the two administrations (3.99 (s.d. = 0.35) vs. 4.08, (s.d. = 0.34), p < 0.005). Conclusion: The authors' evaluation showed that the H-DSS scale was reliable, valid, and responsive. The scale can be used to guide future handheld DSS development and implementation. © 2006 J Am Med Inform Assoc.