•Frontal intermittent rhythmic delta activity (FIRDA) combined with slowing of the posterior dominant rhythm (s-FIRDA) was strongly associated with the diagnosis of dementia with Lewy bodies in routine EEGs from the Amsterdam Dementia Cohort (ADC).

•s-FIRDA demonstrated high specificity for DLB, being positive in 18% of cases, compared to only 1.7% of individuals with Alzheimer’s disease (AD) dementia and 0.8% of all the non DLB diagnoses aggregated.

•These performances would come with a positive predictive value (PPV) of around 90% for a diagnosis of DLB vs AD in settings with 50% pre-test probability, with meaningful diagnostic implications.