Inability to perform activities of daily life is inherent to dementia and an essential component of its severity. Examination of this disability is crucial for diagnosis, management of the patient and family, and evaluation of treatment effects. To examine everyday disability in community-dwelling patients with mild dementia, we developed the Interview for Deterioration in Daily living Activities in Dementia (IDDD) at the memory clinic of the Academic Medical Center at Amsterdam. The IDDD is a caregiver-based measure, which consists of 20 concretely worded items, reflecting the initiative to perform and actual performance of self-care and more complex activities. The original version of the IDDD (1988) was an interview measure, but since 1990 a paper-and-pencil version has been used, which has good construct validity and test-retest reliability, as well as good responsiveness to deterioration over 6 months. In the present study, we examined interobserver agreement among 25 caregiver pairs, which consisted of primary and secondary caregivers. Although the reliability of caregiver reports is often questioned, we found substantial to almost perfect agreement at subscale level and acceptable agreement for most of the items. We conclude that the paper-and-pencil version of the IDDD is a suitable instrument for the description and discrimination of disability among patients with mild dementia still living at home. The IDDD may also be a useful method to incorporate in clinical trials and longitudinal studies.