Dementia is a global public health problem and detection in the primary care setting, particularly in developing countries, is challenging. The aim of this research was to produce the cross-cultural validation of the AD8 interview to the Brazilian Portuguese Language. The original version of the AD8 was submitted to translation, back-translation, and application of the questionnaire to 20 elderly informants for face validation. The AD8-Brazil was then evaluated in 109 community-dwelling elderly with a sociodemographic questionnaire, clinical examination, Mini Mental State Examination (MMSE), Katz Inventory of Activities of Daily Living (ADL), and Clinical Dementia Rating scale (CDR). The AD8-Brazil was compared with the other instruments and with the clinical diagnosis (DSM-IV) for criterion validation. There was significant agreement of AD8-Brazil with diagnosis of dementia (p < 0.001), MMSE (p = 0.047), and ADL (PFisher = 0.004). Also, the AD8-Brazil was able to differentiate the stages of dementia by CDR scale. The reliability was high (alpha = 0.818) and reproducibility analysis showed excellent inter-rater (kappa = 0.889) and test-retest consistency (kappa = 0.814). The AD8-Brazil showed excellent discrimination between CDR 0 and CDR > 0 (area under the curve 86.1%) and between CDR 0 and CDR 0.5 (area under the curve 76.9%). The administration of the questionnaire took 2.3 ± 0.1 minutes. The Brazilian version of the AD8 is a valid, reliable, quick, and easy screening instrument for dementia.