Most of the present screening tests for the detection of dementia fail with mild dementia. Jorm et al. recently presented the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE), a simple instrument with good diagnostic validity that uses a close relative to obtain information on the cognitive decline of a patient. We used a Spanish adaptation of this questionnaire (S-IQCODE) validated in a population-based sample, and a shortened form (SS-IQCODE) obtained after analyzing the items and reducing them to only 17. The S-IQCODE and the SS-IQCODE have greater diagnostic validity for mild dementia than the Mini-Mental State Examination (MMSE) (sensitivity: 86% for both versus 57%; specificity: 92 and 91% versus 84%, positive predictive value: 54 and 50% versus 29%; negative predictive value: 91 and 90% versus 81%) and, unlike the MMSE, are independent of the age, education, and previous intelligence of the subjects. According to the results of this study, the SS-IQCODE could be a useful screening test for the detection of mild dementia in the Spanish-speaking aged population, with greater diagnostic power and less contamination by independent variables than the MMSE.