BackgroundSepsis-associated encephalopathy (SAE) is frequent in septic patients. Electroencephalography (EEG) is very sensitive to detect early epileptic abnormalities, such as seizures and periodic discharges (PDs), and to quantify their duration (the so-called burden). However, the prevalence of these EEG abnormalities in septic patients, as well as their effect on morbidity and mortality, are still unclear. The aims of this study were to assess whether the presence of electrographic abnormalities (i.e. the absence of reactivity, the presence and burden of seizures and PDs) was associated with functional outcome and mortality in septic patients and whether these abnormalities were associated with sepsis-associated encephalopathy (SAE).MethodsWe prospectively included septic patients, without known chronic or acute intracranial disease or pre-existing acute encephalopathy, requiring ICU admission in a tertiary academic centre. Continuous EEG monitoring was started within 72 h after inclusion and performed for up to 7 days. A comprehensive assessment of consciousness and delirium was performed twice daily by a trained neuropsychologist. Primary endpoints were unfavourable functional outcome (UO, defined as a Glasgow Outcome Scale-Extended—GOSE—score < 5), and mortality collected at hospital discharge and secondary endpoint was the association of PDs with SAE. Mann–Whitney, Fisher’s exact andχ2tests were used to assess differences in variables between groups, as appropriate. Multivariable logistic regression analysis with in-hospital mortality, functional outcome, SAE or PDs as the dependent variables were performed.ResultsWe included 92 patients. No seizures were identified. Nearly 25% of patients had PDs. The presence of PDs and PDs burden was associated with UO in univariate (n= 15 [41%],p= 0.005 andp= 0.008, respectively) and, for PDs presence, also in multivariate analysis after correcting for disease severity (OR 3.82, IC 95% [1.27–11.49],p= 0.02). The PDs burden negatively correlated with GOSE (Spearman’s coefficientρ= − 0.2,p= 0.047). The presence of PDs was also independently associated with SAE (OR 8.98 [1.11–72.8],p= 0.04). Reactivity was observed in the majority of patients and was associated with outcomes (p= 0.044 for both functional outcome and mortality).ConclusionOur findings suggest that PDs and PDs burden are associated with SAE and might affect outcome in septic patients.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13054-023-04475-w.