Background: The purpose of the study was to translate the Interview for Deterioration in Daily Living Activities in Dementia (IDDD) into German and to evaluate the construct and concurrent validity in people with mild to moderate dementia. Methods: IDDD data of two pooled samples (n = 301) were analyzed regarding ceiling and bottom effects, internal consistency, factor reliability and correlations with corresponding scales on cognition and activities of daily living. Results: We found minimal bottom (< 5%) and ceiling (≤ 2%) effects, good internal consistency (Cronbach's α > 0.7) and moderate to good factor reliability (0.66-0.87). Low correlations with cognition (Pearson coefficient: < 0.17) confirmed the differences between cognitive testing and activities of daily living (ADL). Minor correlations with other ADL scores (r < 0.2) indicated that different scores cover a different range of ADLs. The original two factor model could not be confirmed. A suggested four factor model distinguishing initiative and performance of basic and instrumental ADL demonstrated better indices of fit and higher correlations with corresponding scales. Conclusion: A four factor model of the IDDD can be used in dementia research for assessing initiative in and performance of basic and household activities of daily living. The findings suggest that ADL scales correlate only poorly and that further development of the IDDD is needed to cover a broader range of ADLs.