Background <p>Dengue is hyperendemic in Singapore and typically presents as an acute febrile illness. Neurological complications, such as dengue encephalitis and encephalopathy, are increasingly recognized; however, dengue-associated posterior reversible encephalopathy syndrome (PRES) remains rare.</p> Case presentation <p>We report a 90-year-old woman with primary dengue virus serotype 3 infection who developed persistent altered mental status during the critical phase of illness. Neuroimaging revealed bilateral asymmetric parieto-occipital vasogenic edema with focal hemorrhage, consistent with PRES, together with small acute infarcts in the deep watershed and left middle cerebral artery territories. Cerebrospinal fluid analysis demonstrated mildly elevated protein without pleocytosis; dengue IgM and IgG were positive, while dengue PCR was negative. She was managed with supportive care with close neurological monitoring. Follow-up imaging at two months showed near-complete radiological resolution accompanied by significant clinical improvement.</p> Conclusion <p>This case highlights two important considerations. First, altered mental status in elderly patients with dengue should not be attributed solely to delirium, and prompt neurological evaluation is essential. Second, dengue infection may be associated with overlapping neurological manifestations, including dengue encephalitis, PRES and ischemic stroke. Recognition of such overlap is important for accurate diagnosis and management of dengue-related central nervous system involvement.</p> Clinical trial number <p>Not applicable.</p>