Abstract Background The adequate information about the functional capacity of elderly populations is a key for the comprehensive assessment of their health status and autonomy. The Lawton IADL (instrumental activities of daily living) Scale is a very often used scale to assess independent living skills, but has never been validated for its use in Spanish-speaking populations. The purpose of this study was to assess the validity, the reliability, and responsiveness of this widely used scale. Methods The validation was based on a prospective cohort of 1,965 patients aged 65 or over who suffered an accidental fall with a hip or wrist fracture as a result. These patients were followed up six months after the production of the fracture. Cronbach’s alpha was used to assess reliability, and exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) for the construct validity. Convergent and discriminant validity were examined by the correlation of the IADL Scale with the Barthel Index, SF-12, WOMAC short form, and QuickDASH questionnaires. Known-groups validity was also studied comparing IADL Scale according to different groups, and responsiveness was assessed by means of effect sizes. Results The mean age was 80.04 years (SD 8.04). The Cronbach alpha coefficient was 0.94. In the EFA, factor loadings ranged from 0.67 to 0.90, and CFA confirmed the homogeneity of the construct. Regarding the convergent validity, all correlation coefficients were higher than 0.40. Significant differences were found according to different groups, supporting known-groups validity. Responsiveness parameters showed moderate to large changes (effect sizes, 0.79 and 0.84 among patients classified as worsened). Conclusions These results confirm that the Spanish version of the Lawton IADL Scale has excellent reliability and validity and a moderate to large sensitivity to change. This study provides a proper validation, not only of the Spanish version of the Lawton IADL Scale, but also of the original instrument.